Connecting a DB connect source system isn’t always as easy as it seems.
RSA13 (or RSA1-> Source systems) and then create a new DB connect source system.

Right mouse click on the newly created source system to set the connection parameters.

Fill in the correct credentials, and you’re there….although…this is what you might think.
For some reason, the settings you’ve just entered are not correctly saved and therefore your DB connect source system is not properly connected….and thus unusable.
You can keep on repeating (in vain) the steps above…or you can hack/add an entry to table DBCON

Just enter the DB connect source system name to this table and then retry to enter the settings (via RSA13)….This time it will work and the settings will be saved!