Fatal error due to conflict with other contributed modules

Can you confirm this problem exists on a fresh Drupal 7 install?

It did NOT exist on the fresh install of 7.14, which I have been running for over 6 months. I run cron automatically @ 3 hours and I just noticed the last run was nearly 3 weeks ago...try to run and get the Fatal error message. Thanks for any help.
Edit: I just remembered that about the same time I began having problems sending private messages...I get AJAX HTTP error code 200...this error pops up as I am typing in recipients name, but if you close and finish typing, the message is sent ok. Perhaps the two are related????????
Jake

This might be due to a conflict with some contributed modules. However, the highest priority is to resolve outstanding bugs that exist in a fresh install.

Fatal error: Cannot redeclare class means that the class has already been declared.

This means one of two things in Drupal: you have two of the same modules in your site's file structure and Drupal is attempting to load both of them or your database registry is corrupt.

Locations you should check for duplication:

1. profiles/*/modules - Keep this version and remove the ones below
2. sites/all/modules - If it doesn't exist in the profiles modules dir, keep this one.
3. sites/*/modules - If it doesn't exist in either of the above locations, you may have a registry conflict somehow.

If you find an offending duplicate module, remove it. Your problem should go away then. If it doesn't, you may have to rebuild your database registry. Install and run the Registry Rebuild drush command to help remedy this issue if it persists.

Wow!!! Outstanding...Finally, after 3+ weeks. I also had 2 copies located in
1) modules/defaultcontent/plugins
and
2) modules/defaultcontent/context/plugins

Like don, I deleted the one in 1) above and cron runs fine...no fatal errors...no errors finding usernames!!
Thank you donpwinston for the help...