Think I found it.

I created a Close buttom in the toolbar, and this seems to be the problem.

It appears that VF7 doesn't like the _mfi_close bar at some situations, and when the GetValue of the StateManager evaluate it, the errors happens.
I put a condition in the

"m.lSkip = EMPTY(WONTOP()) OR SKPBAR('_MFILE', EVALUATE(m.cBar))"

not to run if the m.cBar was _mfi_close, and now everything works fine.

If there are any comments, I'm all ears ... (do you say that in english ?)

Obrigado.