To sell the machine, I want to remove my license or to delete the whole SBS 2011. I tryed via slmgr, but it told me the license I own was not found. Then, I used a tool that listed licenses used and returned 2 - the one I already tryed and another one, that was also rejected by slmgr. So my idea now is to change the license to a trial license. Can I still get one here? What else could I do? All I want is to sell the machine on Ebay without legal trouble. Thanks!

Hi,

You may open CMD with administrator permission, type slmgr /dlv to display detailed license information. Find the activation ID. then type slmgr /upk [activation id] to uninstalls the product key of the current Windows edition. After a restart, the system will be in an Unlicensed state. Detailed information you may reference:
https://technet.microsoft.com/en-us/library/dn502540.aspx

Note that OEM license cant be installed on other hardware.

Or, you may just format the server, and active new server by phone if there is any problem when activating by entering key.

Best Regards,
Eve Wang