I am having this exact problem.
it did NOT help to..
- reboot the phone.
- check for communication issues.
- update.
- deinstall and reinstall. (helped for a short timeframe, but the issue is back)
- initially log in on my.avast on that certain device, log out again and log in again.
my device in question is a samsung i9000gt, rooted with cyanogenmod10. other devices listed on my.avast are an htc magic (perfectly working), the computer i am just writing on (no issues i know about) and a netbook of mine (neither any issues).
i would really love to know i can rely on that anti-theft thing. problem would be: i would in case NEED to fire commands from my.avast, as i cannot do so with sms. these specific phones (samsung with issue, htc without issue) are stuffed with a 2nd and 3rd sim of another 1st sim card inside a siemens C55 which i use for what i think a phone is for: phoning. i need those smartphones as computers and nothing else for work, but am glad that messaging does only work with one of three sims - for which i chose my crash, weather and age resistant and therefor beloved siemens C55. no short message ever will come any close to that samsung (issue) or that htc (working) due to that constellation - thus my antitheft would be useless in case.
please get that fixed soon OR give me another thing to try in case i missed any solutions in this thread.