When I filter the dataset, though column name exists I got an error Cannot find column

In the following lines of the code
foreach (DataRow row in meterDs.Tables[0].Rows)     {                 meterChannels = string.Format("{0} = {1}", Global.MeterIdColumnName, row[Global.MeterIdColumnName].ToString());
                DataRow[] channelRows = ChannelsDs.Tables[0].Select(meterChannels);
In the following line
 DataRow[] channelRows = ChannelsDs.Tables[0].Select(meterChannels);
I got an error Cannot find column [Mtr_T1]
In the debug mode run time values are:
? row[Global.MeterIdColumnName].ToString() "Mtr_T1" ? meterChannels "MeterId = Mtr_T1" ? Global.MeterIdColumnName "MeterId"
Any clue?
Thanks