What does the following WARNING message mean?
Does it cause to fail the migration ?
" WARNING: [XXXX-XX-XXX-XXXXXXXX] Unable to process ACL member 'YYYYYY' on folder 'Calendar' TT:MM:SS Could not find user or group in the Global Address List. "
The WARNING message refers to Notes ACL members who do not have any equivalent in the Exchange GAL; they could be Notes people that have left but the ACL was not cleaned up by the Notes Adminp process, this would normally happen if a user was manually deleted in Notes instead of letting ADMINP clean up the deletion.
The WARNING message can be safely ignored. It is harmless for the migration.