After a lots of test, I found where the problem's append.

I use some TIBStoredProc into a OnCalcField.
This work perfectly when it work on local mode, I mean when
DatabaseName := 'Drive:\Path\MyDB.gdb',

but when I use
DatabaseName := 'MachineName:Drive:\Path\MyDB.gdb',
I got an error 'Invalid request handle'
after 2 or 3 CommitRetaining and only where the OnCalcField are fired.....

I've replaced the TIBStoredProc by an TIBSQL and the problem seems to be

I'm not the only one to get this and it seems always that TIBStoredProc used
in speeded loop is the raison of hang.

I use IBX 4.62  on IB4.2 or IB6 or Firebird with dialect 1

Thanks for your advice.