ERROR 1608: Unable to lookup taxpayer details

When receiving the error message 1608 Unable to lookup taxpayer details, this means that HMRC are unable to process their checks required to pass the UTR entered. This could mean it has been incorrectly entered on the return, the UTR no longer exists (if a company has been dissolved) or if you have entered a UTR for another HMRC service. You will need to contact HMRC to ensure that the UTR entered is correct and to advise how to proceed. 

Below is the extract from HMRC's online document: