IIS HTTP error 404.11 - due to bad filename, plus signs

With URL:    http://server.name.here.com/SIERRA+FUN+FACTS.docx

Got the error message below.  First tried tinkering with mimetype (application/msword) but then decided just to change the filename

http://server.name.here.com/SIERRA-FUN-FACTS.docx

Getting rid of  +  signs solved the problem.

HTTP Error 404.11 - Not Found

The request filtering module is configured to deny a request that contains a double escape sequence.

Detailed Error Information

Module	RequestFilteringModule
Notification	BeginRequest
Handler	StaticFile
Error Code	0x00000000

Requested URL	http://255.255.255.255:80/SIERRA+FUN+FACTS.docx
Physical Path	C:\libraryfiles\Web Documents\SIERRA+FUN+FACTS.docx
Logon Method	Not yet determined
Logon User	Not yet determined

Most likely causes:

• The request contained a double escape sequence and request filtering is configured on the Web server to deny double escape sequences.

Things you can try:

• Verify the configuration/system.webServer/security/requestFiltering@allowDoubleEscaping setting in the applicationhost.config or web.confg file.