Newbie on wikipedia
Something sounds strange as they are both allowed file types. Were you uploading the file at:
Were you logged in at the time?
Can you copy and paste the entire message that you get into a reply to me?
Could the file be a different format but with the .jpg or .pdf extension?
Could you try another .jpg file that is smaller? You can always upload your picture and overwrite it once we figure out the problem.
The more details I have to work with the easier it will be.