Better error message for unexpected non-exception.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@4640 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/parser/ast/Property.java

@@ -200,6 +200,9 @@ public class Property extends ASTElement
 			}
 			throw new PrismException("Unexpected error: " + errMsg);
 		}
+		if (strExpected.startsWith("Error")) {
+			throw new PrismException("Was expecting an error");
+		}
 		
 		// Check expected/actual result
 		Type type = expr.getType();