Those are your escape characters. When you specify your custom connection the module doesn't validate the configuration to allow for maximum flexibility so you'll have to make sure that you create a valid configuration.
In the custom settings there are check boxes that you have to configure to use escape characters in part of your query. You have checked the boxes to use escape characters for the column names. When you check the box to use an escape character you should specify the escape character you want to use.
Leaving the escape character box empty (NULL), it will use that character so instead of escaping as in a normal query: "PRDGRPCDE", it now escapes your columns by doing NULLPRDGRPCDENULL
You should specify an escape character or uncheck the boxes touse an escape character.