Deferred taxes RFUMSV50 error

Hi,

I am trying to run program RFUMSV50 but i keep getting the error Tax code I1 has been deleted or incorrectly changed. Please can you advise on how to resolve this issue.

I have checked that the deferred tax code does exist in the line items and i have not made any changes to the tax code I1.

This is on ECC6, is there maybe a note i need to apply?

Thanks