Mail won't download new IMAP mail, hangs on quit

Hi,
I'm having a problem with my IMAP accounts (Gmail and university). When I open Mail all my messages are downloaded properly, but after about a minute or so no new messages are downloaded. I can still view them via webmail. This just started happening last week. I can't remember doing anything significant to my computer that would cause this. Looking at console I get the message:

 

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