If I set the WriteBufferSize to 4096, it drops out to my Catch, and does not send the data.
Code:
Catch ex As Exception
            MsgBox(com & " not found. Please try other com port(s)")
In the text files that it usually sends, there are no end of line characters. And to put these in would mean a re-write of lots of drivers in for the CAD software that we use. Which I am sure would put an end to this project.

The file size that works was 51 bytes (Size on disk 4,096), ones that don't work are 3.11 KB (3,187 bytes) (size on disk 4,096).