Hi Tim,
IMO, errorcode = 603 does not come from your "Rename File/Folder" function when you rename a folder.
See attached screenshots. The installer tries to rename the c:\test folder to c:\testX
Test 1: the c:\test folder does NOT exist. The function fails, the return value is "0".
Test 2: the c:\test folder exists and is NOT locked. The function renames c:\test to c:\testX (success) and the return value is "1".
Test 3: the c:\test folder exists but is locked. The function fails, the return value is "0".
BTW, return value 603 is not defined for the MoveFile Windows API.
Friedrich