Since it's Vista my guess would probably be that your class failed to register like most people are suggesting. However, recently I had some cases where I was getting "Class not registered" when the class was registered. In my case I was using a .NET User Control that I had created using the interop forms toolkit from Microsoft. I found that if the constructor threw an exception when the SCX was creating the control I got "Class not registered" regardless of the actual error. On the same system a CREATEOBJECT() of the same class would give a different, more useful error. Once I had corrected the error given by CREATEOBJECT() the form would load without having to re register the class.

>I get the following error message when a customer tries to start my program on one of their computers. 4 others are working just fine right next to each other except this one. It is running Vista just like their others are. All bought around the same time according to them.
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>My errorlog reports this:
>Error loading file - record number 8. Mainsportsmanform1 or one of its members. Loading form or the data environment : OLE error code 0x80040154: Class not registered
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>The program will not show the main form and sits there doing nothing basically.
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>I went to record number 8 on my main class and it refers to a Shape on the form base class. This is not even a subclassed shape, just the default box shape around something on my form. Sounds like it is referring to something not disclosed properly.
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>This is the only computer that has had a problem in thousands of installations.