Antonio, I use the fivewin 8.02 with some modifications so if "in many years" mean 2 years, it can be my trouble....
The error occurs when I call a lot of functions from DLL's in sequence, when I use a sysrefresh() or change some window/dialog property between the calls the error don't occur.
xHarbour 1.2.3 + Fwhh 20.2