While browsing the "Crawl Errors" section of Google Webmaster Tools, I discovered a set of very strange 500 errors in reference to my site:

I was able to track down what these characters are, and apparently they are the first two characters in the Unicode Private Use Area. My font just happened to map them to a frog wearing a tiny crown, and a symbol that resembles the numeral 7.

These symbols only appear on the addresses of non-HTML files; office documents, PDFs, etc. - but they do not just appear in the file name.

Where are these symbols coming from, and is there any way I can get rid of them so Google can properly crawl my site?

Some background information:

• Using Web Server running WS2K3 with IIS6 and PHP 5.3.8
• Site encoding is UTF-8
• These symbols don't appear on the page, or in the source