With everyone out of GP run this script in GP:
SELECT * FROM DYNAMICS..ACTIVITY
SELECT * FROM DYNAMICS..SY00800
SELECT * FROM DYNAMICS..SY00801
SELECT * FROM TEMPDB..DEX_SESSION
SELECT * FROM TEMPDB..DEX_LOCK
If any records are returned run these
DELETE DYNAMICS..ACTIVITY
DELETE DYNAMICS..SY00800
DELETE DYNAMICS..SY00801
DELETE TEMPDB..DEX_SESSION
DELETE TEMPDB..DEX_LOCK
Then perform a backup and run check links in GP against the purchasing series. It sounds like some corruption has followed you since GP 2010. Let me know if this helps and if it does not let me know the size of your company database.