Can\'t upgrade

I have tried upgrading from the Free to the Personal plan using Firefox 2.0.0.1, Opera 9.10, and Safari 2.0.4 on an Intel DuoCore MacBook running OS X 10.4.8. On all three browsers, I have tried to Update Credit Card Details, and to Upgrade without first updating (no credit details are presently on file). Both approaches consistently get this error message:

"The page at https://bellamkonda.projects.zoho.com says:
problem ocurred whle updating credit card details
update your valid card details immediately to avoid failed payments in future"

Please tell me what I can do to fix this.

Thanks,
Douglas Swehla
dswehla(at)neuro.gatech.edu
dswehla