MB1B transfer posting error "SL stock in transfer exceeded by 20 PC."

Hi All,

I'm doing a MB1B transfer posting for my materials from 1 storage location to another using movement type 311,

but some of the materials I encountered this error.

"SL stock in transfer exceeded by 20 PC : 'Material name' 'Plant' 'Stor. Loc' "

I went to MB5T to check the materials if it's in the stock in transfer, but they are not in the list.

I've also check in MMBE to check the stock value of these materials, it shows 100 in unrestricted use which is more than what I'm transferring.

May I know what have i missed checking?

Please help and thank you.