Follow these steps :
1. Go to Start ----> Run . Type regedit, then enter .
2. Navigate to HKEY_CURRENT_USER --------> Software ---> yahoo --->pager---->Test
3. On the right page , right-click and choose new Dword value .
4. Rename it as Plural.
5. Double click and assign a decimal value of 1.
Now close registry and restart yahoo messenger and try Multiple Login
