I think this is the HTTP server at the MMS service center saying that the uploaded MMS is too large. My operator places a 300KB limit on messages, though I think if I go over this I get charged for 2 or more messages, but your operator may just say "the message is larger than 200kb, no can send"

Alter the setting in fmms concerned with resizing the picture, so that the whole message gets smaller.

Suggestion for frals: Maybe fmms can accept a maximum size that a message should be and it can repeatedly resize images in the background until the size limit is met, preserving maximum quality?