What is the error number that is logged?
You can use show all delete all in the mean time.
This line is telling in the help document about truncate table...
"If you choose Current Table and the active table when this script step is performed is from an , Truncate Table is skipped and returns an error code. If the active table is from an external FileMaker data source, Truncate Table performs normally"
Seems to me, given your script, that tblHistory is the active table and is from an odbc data source which will result in an error code at this script step.
i haven't tested this but will truncate work if there is a locked record in a table?
Perhaps someone has an uncommitted modified record open in the table...
Next question is whether or not the script in question has delete privileges.
Third, I haen't had problems with go to the layout, but you might try it without that step.
As mentioned by coherentkris, is this NOT a FileMaker table? "tblHistory" is unusual for a FileMaker table name but unusual doesn't mean wrong.
Read the title of the question, dummy...
Reareading the qestion (was it edited?) seems to say this is a SQL table and so it can't be truncated...