The message ‘No Overlay’ relates to AIO and means that UKHO do not include AIO data for that area. To remove the message, you need to turn off the AIO layer on the ECDIS.
Where there is no ADMIRALTY paper chart at equivalent scale to the ENC, UKHO is not able to compare coverage and add additional information. In these areas, the AIO shows a grey hatched polygon labelled ‘No Overlay’.
ADMIRALTY paper T&P NMs may occasionally display within a ‘No Overlay’ polygon if the information has been published for smaller scale paper charts and is also relevant at a larger scale.
Additional information, such as local T&P NMs, may be available in these areas from other sources. When navigating in these areas, seafarers should ensure that other sources of information such as local web sites, Navtex, port notices etc. have been consulted.
Please see the below link for information about which countries include NMs in the ENC updates and which countries are only available in AIO.
ENC TandP NM status (admiralty.co.uk)
If you have installed AIO according to user manual, and you've checked the above file that AIO should be present, and still no AIO found. Please send email with coordinates and screenshot to technical@navtor.com for further investigation.