Thanks Aaron, from that link: community.office365.com/.../835.aspx to convert onpremise mailbox to MEU, there are no steps detailed for Exchange 2010??
I have deleted the failed accounts in office 365 which caused the error relating to "name already being used" and then deleted the failed account from the migration batch and then started migration batch again, its picked up where it left, syncing only wats needed plus the account which was failing before without any issues.
I have checked the sync status and it looks like the incremental sync is working eventhough i have dirysync enabled and running.
now the question is converting to MEU for exchange 2010 necessary of cutover migration, cant seem to find any docs abt this.