[mew-int 3090] error in process filter: mew-imap-command-uid: Wrong type argument: stringp, o

I suddently got the message:

error in process filter: mew-imap-command-uid: Wrong type argument: stringp, o

when trying to update my IMAP inbox. I can't seem to get passed this
point. Is this a known problem with a known workaround?

In my *Messages* buffer I will see:

Setting up Mew world...
Updating status...done
Setting up Mew world...done
Connecting to the IMAP server...done
Communicating with the IMAP server...
error in process filter: mew-imap-command-uid: Wrong type argument: stringp, o
error in process filter: Wrong type argument: stringp, o

Also:

mew-version-number is "6.4.50"

Best regards
//Petter