My guess is that the photo was over in actual file size not dimension size. You were correct in the 640x480 but probably was over the 50kb file size.. In posting photos by the easy post way, the pics are stored in the data base. This is the same data base that house the text postings, To keep the data base to a manageable size, there is a file size limit for photos uploaded. Bigger photos need to be uploaded to the gallery, then you can use the [img] tag (or IMG button above) to link in to your posting.

Sorry for the troubles.