I teach Sage Line 50 v12 at a London FE College and a student brought up a problem which I cannot solve. I have kicked this upstairs to the IT Manager, and he cannot sort the problem either.

The Problem:
If somebody charges a purchase invoice to the wrong supplier, it should be straightforward to change the wrong supplier account to the right one by doing the following:
File
Maintenance
Corrections
Find and highlight the wrong PI transaction
Edit
In Details, select the drop down menu, change the supplier to another
THEN Save.
Unfortunately, when we click on Save, nothing happens!
I spotted this fault on one of the networked classroom computers. I then tried this correction at another workstation in another room and it worked! By the next day, it no longer worked.
On my office workstation it did work until today.
My guess is that there has been some sort of update that is interfering with the ability to save the changes.
Oddly, if I change other things. like the invoice number only, then it will save without any problems.
The IT Manager has tried taking off all restrictions on permissions and it is still not working.
Has anybody any idea what is wrong, or how we can go about getting the corrections feature to work again.
As an aside, he took home a copy of Sage Line 50 to install on his own home PC to see if the feature would work there, where there were not the same applications as at College and it is not working there either!
Help!
John