Maybe i have this problem on another place in the code. The following code is a part of the OnToolTipText function: #ifndef _UNICODE if (pNMHDR->code == TTN_NEEDTEXTA) lstrcpyn(pTTTA->szText, strTipText, 80); else _mbstowcsz(pTTTW->szText, strTipText, 80); #else if (pNMHDR->code == TTN_NEEDTEXTA) _wcstombsz(pTTTA->szText, strTipText, 80); else lstrcpyn(pTTTW->szText, strTipText, 80); #endif This should handle the difference between XP and Win98, right? But it doesn't. My program works fine in XP, but terminates in Win98. Does it matter that i develop in vc7 on XP? And then try to run the exe on Win98? But i think that it should work anyway. Please, someone, help!!