Actually, you don't need expansions in these expressions, so
IF vFileBaseName > vIncrementalExpression THEN ....
should work. If it doesn't check that the two variables have the value expected. You can single step throught the script on the debugger, or add TRACE statements to your script. These will print in the reload progress screen and the in the document log.
TRACE vFileBaseName = $(vFileBaseName);
TRACE vIncrementalExpression = $(vIncrementalExpression );