ImageSize.Width error when checking-in to source control

I'm getting an ImageSize.Width error when checking in to source control. Although I can check in the files using source control, I want to be able to check in using RoboHelp.

Does anyone know how to correct this error?

Value of '272' is not valid for 'ImageSize.Width'. 'ImageSize.Width' should be between 1 and 256.

Parameter name: ImageSize