Column is not mapped to anything

I have an xls spreadsheet that serves as a source. I have a column called "Revenue Data Month". I have it mapped to the WRITER which outputs to another xls Spreadsheet to the same column name "Revenue Data Month". But when it, I get a WRITER error telling me that the Field "Revenue Data Month () is not mapped to anything. But when I look in the Transformer, Validator to the Writer objects, it is mapped. Even previewing the data is showing the data flowing through but in the final WRITER the column is blank.

Perhaps the field name has spaces at the end/beginning?

Yes. For some reason the source file does not have any spaces before or after the column name but when I tell it to assign the heading by using the first line it adds a space in the beginning and end
E.g. Source would look like Revenue Data Month but when I tell it to use the the first line it converts it to [ Revenue Data Month ]
I don't know why an added space is inserted when the source does not have the space.