Backup-Spsite giving error when using -usesqlsnapshot

Good morning,

Some of our site collection backups are failing with a system.exception error, but only when using the -usesqlsnapshot switch on the powershell command.  They work fine when not using this switch.

We need the switch because the backups often last longer than overnight lock site collections during the business day without the sqlsnapshot being used.

Thanks in advance for any insight into this issue!

Kevin