I read about a string/word that did so the Routing crashed but I can't remember which word/string combination it was.
Example:
Microsoft Logging application block and multi-threading - works
Microsoft Logging application block and multi-threading - works
Microsoft Logging application block and multi-threading - works
Microsoft Logging application block and multi-threading - crash!
No it's not banana, but it was a word/string that did so the the routing crashed in every app that used the routing system.
I think I remember this was a known issue but I can't remember where I can find it. Maybe I've read about it on stackoverflow in a comment.
Further to TFD's answer ("con"), it looks like it's pretty much any of the MSDOS reserved device names (Listed under Basic Naming Conventions on MSDN).
I get a HTTP 404 rather than an error though =)
Essentially the list from the extract below:
Do not use the following reserved device names for the name of a file:
CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9