I had a similar issue, the workaround I found was removing all spaces , hopefully may be helpful (may work for some)

I changed my connection string

Data Source=ABCD;User ID=USERNAME;Password=PASSWIORDHERE;Initial Catalog=DBNAMEHERE;Provider=SQLNCLI11;

SERVER=ABCD;UID=USERNAME;Password=PASSWIORDHERE;DATABASE=DBNAMEHERE;Provider=SQLNCLI11;

Worked like a charm for me after that.

Unfortunately , command lines utilities(DTEXEC here thru SQLAgent) are never good in handling any spaces :-(, a chronic issue