If u mean 4D1 mw3 with IW5M, try the following:
Download the Standart-Client, put "LaunchIW5M" and "DB.Networt.Indigo" in the MW3 dedicated Server Folder and replace the old ones with them.
That fixed many problems i had. If it won't won't work, download the whole dedicated server folder again, sometimes there is the prob.
Do u have all iw... and DLC files?