Data Domain Boost viewing backups
For client parameter, please mention the database server name along with FQDN. 

For example if your server name is test and domain is abc.com, then enter the value for Client as "test.abc.com".

Also, please execute the statement  in one Line without any Returns/space:

EXEC @returnCode = dbo.emc_run_delete ' -b "2 months ago" -e
"now" -N mssql -a "DDBOOST_USER=user" -a
"DEVICE_PATH=/path" -a "DEVICE_HOST=host" -a
"CLIENT=test.abc.com"'