Regarding WE20 with partner number

Hi Masters,

While using WE20 I have to give partner number which is same as the logical system name of the destination system ..

for eg: file to idoc scenario ..... here destination system is R3 system .. so i have to give logical system name of r3 system .. but when i am giving logical system name ......its showing message " please enter permitted partner number ." ....

please help me to rectify this problem..

Thanks in advance...

jagannath.