500 Server Error on Export/Import for 1.5.5.1

I absolutely love the Export/Import extension and have been using it successfully for a couple of years now. Today, however, as I'm attempting to export, I keep getting:
500 Server Error

A misconfiguration on the server caused a hiccup. Check the server logs, fix the problem, then try again.
I have read through the forums and have tried a vast majority of the suggestions, but at the most recent try I still am getting this error.

The corresponding Server Log entry recorded:
[Tue Sep 16 10:01:26 2014] [error] [client 129.107.65.218] Premature end of script headers: index.php, referer: http://www.[mydomainname].net/admin/index.php?route=tool/export&token=39be58b1d053f9cb0db78200f48cdfa9

I'm really hoping you can assist me with this.

'Premature end of script headers' could possibly come from an incorrectly 'saved' , 'uploaded' or 'chmoded' File and/or Directory, you should save a modified File in a proper way, UPLOAD it in ASCII Format, not BINARY, and set it to Chmode Value 755, to have it in good order, if it wont work, to lesser secure Chmode Value 775, and test it again. DO NEVER use CHMODE 777, if you have to, to make it work, change your Hoster FAST! Be aware, some files-types have to chmoded to a higher security-level - standard, but this is another story.

If you don't understand what I mean with CHMODE, contact your hoster and add a copy of what I wrote here.
But it could be another Reason as well, it was just an idea, based on a unmodified software. Also, this only works on UNIX/LINUX-based Servers, MS based Server Content cannot be chmoded.
Good Luck
Ernie
openshop.li

Thanks, IP_CAM.
I double-checked my files against your suggestions:
All necessary directories are set to CHMOD 755 and all appropriate extensions (xml, php, html, htm, etc.) are set to transfer in ASCII rather than Binary mode.
My host has no Windows/IIS servers anywhere in their farm although I'm not at all sure what flavor of Unix or Linux they are running.
Thanks again.
crzy