Rockboy on the sansa e260

[CaptainCheese]

I understand that rockboy is a viewer, i have created a folder in my sansa's root called roms, and placed a few backups of the games i already own, they all have the extension .gb
When i goto view them in rockbox, i get an error, the first one says unknown rom size, with an error code, then it says plugin returned error.

Do i not have the right rom extension?

[adscorp]

With Game Boy Color, Usually its .GBC I am not sure about normal GBs.
However, the problem may be that it isn't a valid rom. Just a thought.