The rejection relates to an invalid character in the accounts causing a tagging issue with HMRC.

    If the accounts have been produced within Absolute, in the CT600 form you can click iXBRL in the menu bar / Advanced / Validate XHTML and choose Accounts. This will flag up the invalid character and it's location in the accounts. You will need to amend and then refile. 

If the accounts have been produced using another software package, you need to open the tax return and click file > attachments. Remove the accounts attachment. Through tools > user setup > advanced tick the option for “XBRL contains unusual characters” and click ok. Then reattach the accounts files through file > attachments and try filing online again.