Unknown login key error

Hello, I recently migrated my multisite wordpress installation to a new server. I use subdomains and have WordPress MU Domain Mapping plugin to handle domain redirects.

This has worked amazingly in the past (great tool!). However, since I migrated, I receive an error when logged in and navigate to the front end site. When not logged in, the site works as expected.

The page displays the error “Unknown login key”.

I have not much luck in finding a solution to this issue.

Many thanks in anticipation