RE: Need to restore Multiple Databases on the same SQL Instance

What is the statement generated?

I think you are missing some single quotes.

Try

SET @sql = '-SQL "RESTORE DATABASE ' + @databasename + ' FROM DISK = ''''\\kprod-nas03\sqlbackups\' + @sitename + ''''' WITH PASSWORD=''''fjfelejl'''' SOURCE = '''' + @DatabaseName + '''', MOVE DATAFILES TO ''''D:\SQLData'''' , MOVE LOGFILES TO ''''D:\SQLLogs'''' ,
MAILTO = ''''pam.ozer@kareo.com'''', RECOVERY,
CHECKDB = ''ALL_ERRORMSGS, DATA_PURITY, EXTENDED_LOGICAL_CHECKS'''