COM port redirection

Hi, 

I have a huge problem connecting serial devices to the Windows server 2008R2, through RDC. Two servers running, one does enable us to redirect local serial ports (COM) to the server, the other doesn't. All settings are the same (Local Resources, Ports checked), also security settings are the same (user groups have same permissions).
Does anybody have a clue, what to review? Anybody knows, what is causing this problem?

Thanks in advance, 
Miha