I had a similar problem once, check the UNC **VERY** carefully.
The mistake I was making was something like:
xcopy /c /h /e /d /y g:\dirname\*.* \\server01
I've also had the error when calling a vbscript file with a mistyped name like above.
Dont know if it will help your situation but I had this error and found nothing on google yet it was so simple and stupid....