Hi everyone,
I was scouring the forums here for a solution to a 500 (Internal Server Error) return after installing a new style in my brand new Serendipity installation (1.1.1). Almost all of the posts here referred to the .htaccess file and various things that could be done to address the problem. In my case, however, this was not at all related but it did at least remind me to check the server logs. As it turns out, the server was complaining about the root blog directory being writable by others (mod 0777). I changed it to 0775 (group and owner writable) but it still threw an error. I finally changed it to 0755 and it worked! I put the original .htaccess file in place and Serendipity is so far working fine.
I hope that I can help someone else who may be experiencing this issue. It may have to do with the global PHP settings put up by the host but I can't be absolutely certain of this. In any event, the .htaccess file had nothing to do with the issue in this case.
Good luck!
P.B.
Error 500 (alternate cause and solution)
Error 500 (follow-up)
I just wanted to mention that I switched styles and Serendipity reset the mode of the root folder to 0777, again causing my server to return a 500 error. Again I reset the mode to 0755 and it works fine. Hopefully I won't have to switch styles too often 
P.B.
P.B.