Yes, it depends on the one_letter name:
Im just run the code below to see that restricted letters are:Aa,Bb,Cc,Dd,ee,Ff,Gg,Hh,Ii,Jj,Mm.

***************
ON ERROR ?chr(ia)
fso = CreateObject("Scripting.FileSystemObject")
FOR IA=65 to 90
lccom=chr(ia)+[=fso.GetFolder("c:\temp\")]
&lccom
lccom="fc="+chr(ia)+".Files"
&lccom
ENDFOR
FOR IA=97 to 122
lccom=chr(ia)+[=fso.GetFolder("c:\temp\")]
&lccom
lccom="fc="+chr(ia)+".Files"
&lccom
ENDFOR

<<<<<<<<<<<<<<<<<<<<<
>It seems, the slash should be at the end:
>fso.GetFolder("c:\test\")

I just added:

lcfolder = LEFT(lcfolder, LEN(lcfolder) - 1)

to my test code and it ran fine also. It was a long path to boot, so I don't think that the trailing backslash is a necessity. FWIW, GETDIR() returns a path with the trailing backslash.