One Time Service

Dear Friends,

Just like there is a one time customer and vendor account group for vendor and customer who we deal with only once a while.

Is there something like one time service in MM.?

We have few services defined in AC01 and attached a valuation class to each service. What if we need to pay for some service (one time), there shouldn't be a need to create a service master.

When we create the PO for such one time service not defineed in AC01, it saves the PO, but does not allow us to perform the Service entry sheet.

Error it throws is: Account determination for entry CAAI KBS 0001 not possible. (CAAI - is our Chart of Accts), what is it that is related with key KBS in GBB of OBYC?

Thanks

Sanjay