system issue during budget check commitment item

Dear PS experts,

     while attaching a material to a specific activity the budget have to check the PR value as i activate commitment management in controlling area.

but i have an issue as when the material (( PR for network )) i have an information window told me that ((error in commitment check . see costing log)).

but when i make this material (( PR + reservation for WBS )), the system doesn't raise this error message and i can save the project.

Note : i have another material that the system raise error in commitment check in the two ways (( PR for network and PR + reservation for WBS )).

So what could be the problem with the other materials ??