Thank you Francois for your prompt reply!
I am using meg/meg1 brainstorm on a workstation in MNI, so it is relatively up-to-date (the version in the snapshot is Dec. 1, 2021, and I could update again to Dec. 28th), not sure why the icon is not loaded well!
Yes, this is an old database. Thank you for your suggestion, after restarting brainstorm and reloading the database, the error message changed it was related to missing the source .meg4 file and I could fix it.
Thanks a lot,
Soheila