For the past 3 days I've been using Yosemite with virtually no problems. It actually runs better for me than 10.9 did. Suddenly today I've been having issues with iMessage. It will not let me sign into iMessage using my Apple ID to send and receive texts. I called Apple and they said that my ID is fine, which I know because it's been working fine on my iPhone and iPad. The error either says to check my network connection (which I've done) or to call Apple with a support number. Just wondering if anyone else has had this problem?