When adding my ID3 tag full of info, with an image, save it, then try to upload that same audio into my video editor, Camtasia 8, it gives me an error. (Don't have error message on hand, I can provide if needed).
Next, when importing the same ID3 tagged audio into a music program (DAW) such as FL Studio, it is again giving me a similar error. Not with a pop-up window.. but it's not recognizing the audio at all!
Could check your files with MP3val or Mp3check first?
It looks as though your programs cannot cope with v2 tags and interpret them as audio data.
If the checking does not return any errors try to write only v1 tags - these do not have pictures, though.
Go to File>Options>Mpeg
and set the write option to only V1 to get plain v1 tags.
And: It would be very unusual if MP3tag caused the problems as it usually works ok but some (other) players / editors behave strangely.