Whether you're playing SDM in regular CoD or CODUO, you MUST put the "user-SDM_ServerAndClient_v1.2_GOES-IN-MAIN_xXezekielXx.pk3" file in your 'Call of Duty\Main' directory.  Additionally, you'll want to put the "user-SDM_ServerAndClient_v1.2_GOES-IN-UO_xXezekielXx.pk3" file in your 'Call of Duty\uo' directory if you're playing SDM with UO.  Either way though, remember, you should always have the "GOES-IN-MAIN" pk3 in your 'Main' folder.