>No that's not it! After adding the function if.prg I found out that if.prg is called at a line like: "USE (File1) IN 0 ALIAS Table1" where File1 = "Path\Filename.dbf"

Post back the _exact_ line of code and the values of any variables when the error occurs. Best way to do this is to put a breakpoing on the line of code, and check the values in the watch window.