Hi Christian, I encountered this error-message. I have a strong feeling that this error is related to previous reports, see . my email dd 13-05-2013 and 03-12-2014 My program is heavily recursive so it is hard to create a running snippet but I will try. Hopefully in the mean time you can have a look at the error. TIA, Rob Stapper ===================================== Error: Improper use? Potential bug? Your feedback is welcome: Contact: basex-talk@mailman.uni-konstanz.de Version: BaseX 8.6.1 beta 855f949 Java: Oracle Corporation, 1.8.0_31 OS: Windows Vista, x86 Stack Trace: java.lang.RuntimeException: $seq_1644 as (function(*))? index: 87, slot: 9 at org.basex.util.Util.notExpected(Util.java:62) at org.basex.query.var.QueryStack.pos(QueryStack.java:101) at org.basex.query.var.QueryStack.set(QueryStack.java:123) at org.basex.query.QueryContext.set(QueryContext.java:756) at org.basex.query.expr.gflwor.Let$LetEval.next(Let.java:184) at org.basex.query.expr.gflwor.GFLWOR.item(GFLWOR.java:58) at org.basex.query.expr.ParseExpr.toItem(ParseExpr.java:488) at org.basex.query.expr.ParseExpr.toArray(ParseExpr.java:663) at org.basex.query.func.fn.FnApply.value(FnApply.java:32) at org.basex.query.func.Closure.item(Closure.java:288) at org.basex.query.func.Closure.value(Closure.java:321) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invoke(FuncCall.java:87) at org.basex.query.func.FuncCall.value(FuncCall.java:159) at org.basex.query.value.item.FItem.invokeValue(FItem.java:44) at org.basex.query.func.fn.FnApply.value(FnApply.java:38) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invoke(FuncCall.java:87) at org.basex.query.func.FuncCall.value(FuncCall.java:159) at org.basex.query.value.item.FItem.invokeValue(FItem.java:44) at org.basex.query.func.fn.FnApply.value(FnApply.java:38) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.expr.If.value(If.java:128) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invokeTail(FuncCall.java:123) at org.basex.query.func.FuncCall.value(FuncCall.java:60) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invokeTail(FuncCall.java:123) at org.basex.query.func.FuncCall.value(FuncCall.java:60) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.expr.If.value(If.java:128) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invokeTail(FuncCall.java:123) at org.basex.query.func.FuncCall.value(FuncCall.java:60) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.expr.If.value(If.java:128) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invokeTail(FuncCall.java:123) at org.basex.query.func.FuncCall.value(FuncCall.java:60) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invokeTail(FuncCall.java:123) at org.basex.query.func.FuncCall.value(FuncCall.java:60) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.expr.If.value(If.java:128) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invokeTail(FuncCall.java:123) at org.basex.query.func.FuncCall.value(FuncCall.java:60) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.func.StaticFunc.invValue(StaticFunc.java:182) at org.basex.query.func.FuncCall.invoke(FuncCall.java:87) at org.basex.query.func.FuncCall.value(FuncCall.java:61) at org.basex.query.expr.TypeCheck.value(TypeCheck.java:131) at org.basex.query.func.Closure.item(Closure.java:288) at org.basex.query.func.Closure.value(Closure.java:321) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invoke(FuncCall.java:87) at org.basex.query.func.FuncCall.value(FuncCall.java:159) at org.basex.query.value.item.FItem.invokeValue(FItem.java:44) at org.basex.query.func.fn.FnApply.value(FnApply.java:38) at org.basex.query.expr.gflwor.GFLWOR.value(GFLWOR.java:72) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invoke(FuncCall.java:87) at org.basex.query.func.FuncCall.value(FuncCall.java:159) at org.basex.query.value.item.FItem.invokeValue(FItem.java:44) at org.basex.query.func.fn.FnApply.value(FnApply.java:38) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.expr.gflwor.Let$LetEval.next(Let.java:182) at org.basex.query.expr.gflwor.GFLWOR$1.next(GFLWOR.java:95) at org.basex.query.expr.ParseExpr.item(ParseExpr.java:51) at org.basex.query.expr.ParseExpr.value(ParseExpr.java:65) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.value.item.FuncItem.invValue(FuncItem.java:117) at org.basex.query.func.FuncCall.invoke(FuncCall.java:87) at org.basex.query.func.FuncCall.value(FuncCall.java:159) at org.basex.query.value.item.FItem.invokeValue(FItem.java:44) at org.basex.query.func.fn.FnFoldLeft.value(FnFoldLeft.java:22) at org.basex.query.QueryContext.value(QueryContext.java:405) at org.basex.query.expr.gflwor.Let$LetEval.next(Let.java:182) at org.basex.query.expr.gflwor.GFLWOR$1.next(GFLWOR.java:95) at org.basex.query.scope.MainModule$1.next(MainModule.java:121) at org.basex.query.QueryContext.cache(QueryContext.java:635) at org.basex.query.QueryProcessor.cache(QueryProcessor.java:113) at org.basex.core.cmd.AQuery.query(AQuery.java:86) at org.basex.core.cmd.XQuery.run(XQuery.java:22) at org.basex.core.Command.run(Command.java:257) at org.basex.core.Command.execute(Command.java:95) at org.basex.gui.GUI.exec(GUI.java:471) at org.basex.gui.GUI.access$3(GUI.java:425) at org.basex.gui.GUI$6.run(GUI.java:413)