This is caused by either the Legacy or Basic GL module not being unlocked.  To resolve please contact support for an unlock code and provide what GL module you're organization uses (Legacy or Basic).  Once a case is created and you're provided with an unlock code please follow the below steps to resolve:

1.    Log in and select Tools > Unlock Optional Modules
2.    Select the manual option and enter the below unlock code then click enter
3.    Select Tools > Refresh Shell Navigation and then go to the Revenue functional area where we should find the post to GL process now.