The error message "Unable to open session file" may appear when users try to login to MAS 90 or MAS 200.
While this may indicate a corrupt session file in the ..\mas90\home\session folder, in some instances it has indicated improper user rights.
Make sure all MAS 200 users have full rights to the \mas90 folder and all subfolders.
Browse the various folders within Sage MAS 90 or 200 and check their security rights. Make sure that all rights are enabled. After enabling all rights rember to apply them and re-start Sage MAS 90 or 200.
IMPORTANT NOTE TO IT ADMINISTRATORS: Please take the time to check this important step. If you can get the system running with full permissions on these folders you can always go back and g-r-a-d-u-a-l-l-y restrict the user rights on the folders.
Sage MAS 90 and 200 do require full rights to the \mas90 folder and ALL subfolders. Modify these security permissions at your own risk (usually the only downfall is numerous "cannot open" type error messages).