Hi,
I suggest that you open a support request but before sending the request, I think it will be helpful if you select 'Preferences' from the 'ooVoo' menu, select 'Support' and check the 'Enable debug logging' option. From the 'ooVoo' menu select 'Quit' and sign in again. Afterwards have someone call you and if you fail to join the call, the problem should be written into the log file. Attach the log file with your support request (you can easily find the location of the log file from the 'Support' page).
Please note that the 'Enable debug logging' option is only available in the new MAC version 1.7.
Thanks for using ooVoo,
Marvin