Win7 default "My Documents" location folder

When I try to map my default "My Documents" folder location to a folder located on another,in the "properties" of the "My Documents" folder there should be tab named "Location" which is missing.

I've a second PC on which I made the same operation and it worked perfectly. The tab was there and I've setup the default location of "My Documents" on another drive.

The first PC, the one on which it doesn't work runs Win7 64 professional , the second runs on Win7 32 professional.

How can I map "My Documents" to one of my other drives? I am getting mad with this and I've already spent month trying to find a solution... but nothing.

Thanks in advance for your help!