Diagnosis
You want to allocate material components to an operation. However, nomaterial to be produced and thus no BOM has been allocated to therecipe. For this reason, you cannot allocate material components.

Procedure
If you want to allocate material components to the operation, firstallocate the desired material to the recipe on the recipe overview.
To do so, choose Goto -> Recipe overview and thenRecipe header -> Mat./rec. allocation.