YOUR site does not use those characters, but the site where that link came from DOES use those characters. That's why Google was looking for that URL, it's not because of your site, but some other site like a scammer scraper phony SERP site has a link to your site and when Google crawled them and found your URL there, they came to your site looking to index that URL where Google was met with an error from an improperly formatted URL.
It might also be the 404 URL that Google generates to verify your site when you first signup to Sitemaps. A lot of people forget, that as part of the verification process, GOogle sends a purposefully incorrect URL to your site to make sure you have a true 404 Page Not Found page. SO it could be that also.
As we have found with our site, our links appear on thousands of those phony SERP scraper pages, which are merely repackaging the top 10 overture or top 10 Google adwords pay per click results for a particular keyword.
So the quesiton is, do you advertise on Adwords, or Yahoo's pay per click searches?
If so, what you're seeing is probably remnants of a scammer's adwords or Overture affiliate code used to generate the URL leading to your site from his phony SERP page. It's easy to spot the overture and Google links to your web site on these phony SERP pages. Here's how:
Let's say you search for widgets on Google, and click on one of the results that looks promising to you. Turns out you just land on one of those SERP pages that is just another listing of 20 search engine results, with some adwords thrown in. Then you see your site listed there.
You'll see the link to your site that when you mouse over it, the browser status bar shows you www.example.com, but if you actually do a view source on the scammers web page, you'll see the URL is some real long URL like the one you showed in your posting to start this thread.
Usually though, it will be like 2 lines long, and start like this:
Scammers are sneaky this way, they tell the browser to show you one URL to trick you into thinking you are going straight to your site, but in the HTML they actually use the lengthy Google ADwords or Overture PAID link to your site. So people click on the "link to your site" not knowing it's actually a sponsored link, that you are paying for. The affiliate links from Google adwords and Overture are long, with tons of encoded characters.
So why did you get the 500 error?
It could be they are trying to wreck your server on purpose, or they just screwed up generating the code for your site, and your server did not like the format, and choked on it.
THe fact that you got the 500 error and NOT the 404 error makes me think that this was NOT Google performing the 404 test as part of verification. But check your log file and see if this error occurred at the time you were performing your initial Sitemaps verification.
My gut feeling says this was a scammer pulling some kind of trick that back fired on him. He won't earn any money as an Adwords affiliate if the link does not go through!
Hope this helps!
[edited by: JeffOstroff at 1:11 am (utc) on July 30, 2006]