It's worth a try to delete all the files in the core/cache directory and clear your browser cache and cookies.
I should have mentioned that you can log in again by editing the modx_system_settings table in PhpMyAdmin (select your MODX database) and changing the value of captcha.enabled from 1 to 0.
You'll have to delete the files in the core/cache directory and clear the browser cache and cookies again after doing that. That will turn Captcha off and you can log in again.
FYI, Captcha is not particularly useful these days, IMO, because most of the bad guys have software that will decode the Captcha image. So having it on annoys regular users with very little gain in security. Using a strong password with no dictionary words is much better protection and, if you want more security, you can use a random string of letters and numbers for the admin username and (in Revolution) rename the manager and core directories and move the core directory outside of the web root.
[ed. note: BobRay last edited this post 15 years ago.]
I was facing the same problem, and clearing the cache worked for me. After clearing the cache folder i am able to login to the manager. Thanks bob
