SqlDataAdapter.Fill - Timeout expired. The timeout period elapsed or the server is not responding

My C# application is showing ominous behaviour.

The application is working perfectly fine for a specific Installation. But it's giving me this exception in another..
- SqlDataAdapter.Fill - Timeout expired.  The timeout period elapsed Prior to executing the query or the Server is not responding.

I've been searching all day for a solution and cant find anything helpful.

The c# Code is

            DataTable dt = new DataTable(tableName);
            try
            {
                using (SqlDataAdapter da = new SqlDataAdapter(SqlQuery, conn))
                {
                    Console.Write(SqlQuery);
                    da.Fill(dt);
                }
            }
            catch (Exception ex)
            {
                throw new Exception(string.Format("Foo String there is nothing good Happening {0}", ex.ToString()));
            }

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The SQL is : SELECT * FROM FooTable WHERE ColumnA=0 and ColumnB='15'

Every Google post I've been looking at is about "increase your command timeout". Which makes me almost give up hope.

The same SQL in SSMS Returns only 1 row and I've seriously no idea what is going on.

I've attached a Debugger to the process and can definitely say the code is reaching the Console.Write as a breakpoint.
The exception is thrown at the fill method line.

I'm highly thankful for any responses.