Before a client can use your custom interface, the proxy/stub DLL for the interface must be installed in the system registry. Registering the proxy/stub DLL involves creating a .REG file and running REGINI. In the following entries, notice that the IID for ICustomInterface is the same as the CLSID for the proxy/stub DLL.
\Registry\MACHINE\SOFTWARE\Classes\Interface\ {7ACC12C3-C4BB-101A-BB6E-0000C09A6549} = ICustomInterface \Registry\MACHINE\SOFTWARE\Classes\Interface\ {7ACC12C3-C4BB-101A-BB6E-0000C09A6549}\ProxyStubClsid32 = {7ACC12C3-C4BB-101A-BB6E-0000C09A6549} \Registry\MACHINE\SOFTWARE\Classes\CLSID\ {7ACC12C3-C4BB-101A-BB6E-0000C09A6549} = ICustomInterface_PSFactory \Registry\MACHINE\SOFTWARE\Classes\CLSID\ {7ACC12C3-C4BB-101A-BB6E-0000C09A6549}\InprocServer32 = proxstub.dll