.htaccess error / Internal Server Error 500

We’ve been running a BlackBerry site at https://www.bbleaks.com, but have recently been experiencing an issue with our .htaccess file and getting consistent 500 errors.

I have deleted the .htaccess file, changed it to .txt format, and everything else imaginable. I thoroughly checked through plugins and other code, and think the problem is with the permalinks and the .htaccess file. Our current permalinks structure is set to /%post_id%/%postname%

Sometimes the .htaccess file with take the same code and multiply it a hundred times within the same file. This causes a complete and constant 500 error until the .htaccess file is deleted.

How can this be fixed? Please help, as this has become extremely frustrating and we’re loosing hundreds of traffic data. Thank you greatly in advance!