Add an error message suggesting to convert to a later NWB format

[legouee]

Should fix #1131

[pep8speaks]

Hello @legouee! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers:

Comment last updated at 2022-09-07 12:43:39 UTC