I won't lie--you have me a bit stumped on this one. There are only 2 things that come to mind:
First, it's possible that the login is failing and the result is another CAPTCHA challenge. Are there any "special" characters in your password that perhaps we are not handling correctly? If so, try temporarily changing your Google account's password to only letters and numbers. Then log into VC with the new password to see if it works.
Second, reinstalling the app may help. To
fully remove it, follow the instructions in this FAQ:
http://voicecentral.riverturn.com/faq.php#question15Please also perform step 10 so that all offline data is removed. Then add the app to your home screen again to see if the problem is resolved.