Why do I get an 'Invalid Path Character' error?

In Windows, you can create a folder called c:\who,what\. You can also create a folder with 'bad' characters, e.g. commas, in the name using FileSystemObject (of course, assuming sufficient permissions): 
 

<%      set fso = CreateObject("Scripting.FileSystemObject")      fso.CreateFolder "c:\who,what\"      set fso = nothing  %>

 
Now, when I try to do the following, I get an error: 
 

<%      set fso = CreateObject("Scripting.FileSystemObject")      fso.CreateFolder Server.Mappath("/who,what/")      set fso = nothing  %>

 
What's up with that? Here is the error I receive: 
 

Server.MapPath() error 'ASP 0173 : 80004005'   Invalid Path Character   /<file>.asp, line <?>   An invalid character was specified in the Path parameter for the MapPath method.

 
The initial response I received from Microsoft was that the path passed to MapPath was perhaps 'protected' due to possible conflicts with URLEncode or HTMLEncode. I commented that a comma is a perfectly valid URL and HTML character, and that neither Server.URLEncode nor Server.HTMLEncode really altered its appearance. They said they'd keep digging, and that they might even have to look at the code (gasp!). 
 
So, while we wait for an official response, which I'm promised is forthcoming, I can suggest a workaround. Namely, use Server.MapPath() to obtain the root, and then build out using "local" folder paths. For example: 
 

<%      set fso = CreateObject("Scripting.FileSystemObject")      fso.CreateFolder Server.Mappath("/") & "\who,what\"      set fso = nothing  %>

 
While I'm not optimistic this limitation of classic ASP will ever get fixed, I have to assert that if I can create a folder with certain characters in the name in Windows or using FileSystemObject, I should be able to get the path of that folder using Server.MapPath. 
 
FWIW, here are the characters that cause the Server.MapPath method to fail: 
 

CHR(0)  CHR(9)  CHR(10)  CHR(11)  CHR(12)  CHR(13)  CHR(32)  CHR(38) &  CHR(34) "  CHR(42) *  CHR(44) ,  CHR(58) :  CHR(60) <  CHR(62) >  CHR(63) ?  CHR(160)

 
Another case where you may come across this problem is something like the following: 
 

<%      Server.Transfer("/file.asp?foo=1")  %>

 
This is because server.transfer internally performs a server.mappath() (for some reason), and it can't take the ? character... 
 
For whatever it's worth, I couldn't get & to fail on a server.mappath call, using Windows 2003 Server. However it is listed above because others have reported it as being an issue (I imagine on earlier server versions, or maybe a client OS like Windows 98).