https://help.wolterskluwer.co.uk/Customers/s/article/11487


Some of the online filing validation error message refer to box numbers in the tax return and these can
often be a bit of a mystery when trying to discover where the error actually lies.

The box numbers are broken down into two parts. The first 3 letters refer to the type of income page
and the numbers refer to the actual box number within those pages.

The following list should help to provide some clues as to where to look for the potential errors in your
tax return.
A11SA100Address details boxes
AILSA101Other information
AOISA101Other UK income
AORSA101Other tax reliefs
ASESA101Share schemes
CALSA110Tax calculation 
CGTSA108Capital gains tax
EMPSA102Employment 
FINSA100Finishing your return
FORSA106Foreign income
FPSSA104FFull Partnership
FSESA103FFull Self-Employmen
INCSA100Standard income 
LUNSA103LLloyds underwriters 
MORSA102Minister of religion
NRDSA109Residence, remittance etc
PROSA105Land & Property
RELSA100Reliefs
SPSSA104SShort Partnership
SSESA103SShort Self-Employment
TRUSA107Trust and Estate
YPDSA100Personal details boxes
YTRSA100Tick boxes on page 2
Using the above examples, you can then work out that a reference in the error message to box CAL14 would
refer to box 14 in the Tax Calculation pages on the tax return. A reference to box SSE33 would refer to box
33 in the Short Self-Employment pages on the tax return, and so on.

Most of the box numbers displayed in the error message will be hyperlinked. This means that clicking on it will
take you straight to that box in the tax return if it is present. If a box is not present in the current tax return,
it will just take you to page 1 of the return. By cycling through each hyperlinked entry it should be possible to trace the error.