I was bemused to discover that P11Ds filed online with no C1ANIC items were being rejected for C1ANIC errors.
When I contacted HMRC's helpdesk I was told to monitor their website's 'Issues' section for updates about the fix.
If you click on the link within the 'Service Availability & Issues' link in the bottom right-hand corner of HMRC's Home Page & then click on 'PAYE' you'll see this message displayed:
"Expenses & Benefits End of Year Returns P11D and P11D(b)
We are aware that some customers are receiving the following error messages;-
7790 - The NIC payable value must equal 12.8% of the total benefit.
7700 - The Cash Equivalent value must equal the Cost less the Amount Made Good
Both these errors are under investigation with out IT partners. We will update this page as soon as we have more information.
HMRC apologises for any inconvenience caused."
So, be prepared to file paper returns if the online system continues to frustrate!