Research indicates that this error is caused by ASP's Request.BinaryRead method, which FileUp calls internally to read the upload stream, in conjunction with using SSL.
The line number stated in the error message will reference the line where FileUp's Form collection is first accessed. This is the point where FileUp calls Request.BinaryRead to process the upload.
Service pack 3 for Windows 2000 may resolve the problem. Please download and apply the latest service pack available from Microsoft for Windows 2000.