.htaccess causes me 500 Errors…

Hello.

I have been using wordpress for quite a while now. And in the last 3 weeks, my website was always showing some 500 and 503 errors. I didn’t know what was that, so I asked my hosting company for some help, and nothing, after trying many different things (disalow bots, etc…), I decide to take a closer look to the error.log file on my server… there was planty of mod_rewrite errors, so I deleted the .htaccess file and my website was running fine.

Now anytime the htaccess file is running on the server, my website is down… I works fine for a limited amount of time and then I have to remove the file. Is there anything wrong with the code? Permalink structure? Apache incompatibilities??

Thank you for your help.
Michael.