Why is the save token wrong?

Question

Joomla

Good day to all!
There is a site on Joomla 2.5.28 (don't ask why such an old version, just the bosses don't want to change) and VirtueMart 2.6.6 is installed in it. There are categories, products, etc., respectively, as it should be in an online store.
And recently such a problem has begun: I add "modules" for the main product (for example, I add a wall cabinet for a kitchen) and when saving, it gives an error "Invalid Token save".
I don't know what to do... please tell me how to solve this problem!)
PS: This problem started about a week ago.

Answer 1

It turned out that the problem was not entirely in the token. There was a limit on max. the number of sub-products in the product. And because of this, this error came out