C# WinForm ErrorProvider tooltip display problem

I have problem with a C# Win Forms app that uses the ErrorProvider class to provide input validation feedback to the user. On my development workstation (WinXP Pro + Visual Studio .NET 2003), when I run the app by itself or from VS, everything works fine... the ErrorProvider tooltips display correctly, etc. However, on other systems (e.g., Win 2003 Server, or even another PC running XP Pro), after the app enters validation mode, the error tooltips don't display at all when the pointer is hovered on the error icon. Furthermore, if the error icon is located close to the lower or rightmost edge of the form, it looks like the tooltip is actually being displayed behind the form, since a portion of the tooltip text is visible in the area just beyond the edge of the form. Is this a Microsoft bug that has been fixed recently via Windows Update? Would this explain why the problem does not exist on my workstation, but does on others. I haven't found any posts thus far for this and would appreciate very much any help. Thanks.