Simple way to do this is:
- Go to START->RUN-> Type 'regedit' and press ENTER.
- Then navigate to 'HKEY_CURRENT_USER\Software\Yahoo\Pager\Test'
- Now in the right pane right click New->DWORD Value. Name it as 'Plural'.
- Now Double click the the Plural DWORD you created & set the value to 1.
Now try login using two id's in a single machine.