Have you watched the Load during these issues? Ordinarily these buttons work all the time or Don't work all the time (if there's a bug). So having them work sometimes but not others is generally a sign that you have load issues with your server. Does the problem occur during the busiest portion of your day?
If not, it may be worth the effort to upgrade to Vicibox 4 and see if there is an improvement (not to mention the cool new toys like Quality Control ... in the later versions ...). You can also just upgrade in place to get the later version if you like the CentOS system presently installed. But remember that GoAutoDial has that pretty screen you will lose.