Twitter help required!

I'm getting this error message from Twitter on my Mac, even if I only try to tweet one word. Help! I feel disenfranchised. I can only Tweet from my phone. I've restarted Twitter and the Mac. No joy.

Opening and ending tag mismatch: link line 9 and head
Entity 'rarr' not defined
Opening and ending tag mismatch: img line 35 and div
Entity 'copy' not defined
Opening and ending tag mismatch: div line 32 and body
Opening and ending tag mismatch: body line 11 and html
Premature end of data in tag link line 8
Premature end of data in tag meta line 6
Premature end of data in tag meta line 5
Premature end of data in tag meta line 4
Premature end of data in tag head line 3
Premature end of data in tag html line 2

Any suggestions?

Update: fixed - it must have been a Twitter-end problem. Thanks for the people who replied. Except for @bruno_di_gradi.