unable to reserve inventory for sales order [AX 2012 R2]

Hi everyone,

i'm not able to reserve inventory for a sales order. The SO is "Open order" and confirmed, the inventory is available. But if i try to reserve the inventory for the sales line i'm not able to enter a qty. There is no error message or warning either. What did i forget?

Edit:

The order doesn't show up in Inventory and Warehouse management -> Periodic -> Release sales order picking either.

Edit2:

I'm able to reserve another sales line (another item) on the same order. So there is maybe something different with the item. Now the order shows up in "Release sales order picking" too.

Regards

Nils