Filesharing problem between windows 7 the Freecom Network Media Player Wlan - 350

Hi,
I have a filesharing problem between my windows7 machine and my Freecom Media player (a hardware media player to connect to a television). The freecom mediaplayer recognizes my windows 7 PC, but it says that no directories are shared. (but of course I shared some directories in win 7).
I have also an old XP pc and file sharing between the Windows 7 machine and the XP machine is no problem.
What I already tried:
*turning off firewall
*enabling the guest account
*giving file sharing rights to everyone and to the guest account.
*enabeling file and printer sharing
*turn off password protection for file sharing
*create a homegroup
*leaving the homegroup again

File sharing between my Freecom media player and my old Win XP PC is possible.
Before windows 7, I had Win Vista installed on my new PC. File sharing between the media player and the new PC with windows Vista was also possible.

I have build 7100 of Win7 RC.

I hope somebody can help me ? I think it might be a problem with rights of the guest account or something like that. Maybe an extra security feature of windows 7 that was not yet present on XP and Vista