We are aware of the issue where using the Rank Checker feature on too many KWs at once can cause an 'endless captcha'.
If you'd like to avoid Captchas from popping up, try to limit usage of the Rank Checker feature while we work on finding a way to fix this bug.
Also, another way to avoid Captchas when using the Rank Checker is to make sure that you're not checking for keywords where your site is ranking 300+ (around page 30) in the Google search results pages.
If you're currently experiencing Captchas repeatedly popping up whilst using LongTailPro, Google may have temporarily blocked your IP. Try closing the software and waiting an hour or two and this temporary ban should be lifted.
We apologize for the inconvenience, and we hope you understand that we're actively working on a way around this particular issue. We anticipate that a workaround will be available in about two months from now.
If you're having ongoing problems with Captchas whilst using the Rank Checker, please contact our Support Team and we'll try our best to help you resolve the issue.