Or you can go into the TATEMS installation directory:
C:\Program Files (x86)\TATEMS 2005\
...and rename the file called "OpeningScreen.jpg" to OpeningScreen-Old.jpg
The entire error message may say:
The expression On Load You Entered as the event property setting produces the following error: TATEMS 20/20 Version 4.6.19 doesn't support this format of the the file 'C:\Program Files\TATEMS 2005\OpeningScreen.jpg.' or file is too large. Try converting the file to BMP of GIF format.
~ This expression may not result in the name of a macro. the name is a user-defined function. Or [Event Procedure]
~There may have been an error evaluating the function, event or macro
The folder location and the TATEMS version number may be different in your case.