The scenario is:
Three products available for request in IT Shop: A, B and C.
For products A and B there is a dependency for product C and it is compulsory to request this service item at the same time as the others.
However, product C has already been requested and this request is approved.
Following that product A is requested.
IT Shop tries to create an additional item in the shopping cart for product C, but that fails because this product has already been assigned to the Employee.