1.2.1 admin - impossible to save user profile

Hi,

I need help to fix a problem in an old CB version 1.2.1.

Since one week it is impossible to save user profile from the backend admin.
It is possible to save the profile from the Frontend no problem.

I believe something is not anymore compatible with browser.
Could you point me the diff between saving the profile from the frontend vs backend?

I'm looking for a fix without updating CB cause the actual setting is very complicated, a lot of custom code and a lot of component related to CB.

The DB is ok, the problem start with IE and is not compatible since almost 1 year, Firefox is not compatible since a few weeks and Chrome is no more compatible since one week.

I know it is an old CB version, they plan to update the whole site to the latest versions but they are not ready to update now.
So please any help is welcome.

Sorry impossible to go back version wise and provide any kind of support - that's what new versions are for.

Also, if you made changes to core code you are more or less on your own.