Dynamics GP - Users login and instead of initializing, GP hangs at a blank white screen

We experienced this issue due to a single faulty SOP transaction that could not post properly.
A single user was trying to do a transaction post on a specific invoice, and caused the entire database to lock up.
GP would get stuck attempting to post this bad invoice.
No other users could log in.

The only solution was to restore to a previous backup file, and run a check links and reconcile to fix the transaction.
The transaction itself was then deleted and re-entered manually.
This resolved the issue.

You can also try deleting any stuck transaction-level postings by running this script.

delete from sy00500 where  bchsourc like '*%'

It also corrupted our Reports dictionary,and that had to be restored from a backup.