I don't have the F2100D, but I do have an F3400DT and I would assume the programming software is somewhat similar.
What I found is you may need to setup a zone first (if they exist for the 2100D), then program a channel(s). To enter a channel or change anything else on the line, you need to double click on the RX frequency and enter one in. THEN, you can modify anything else on that line.
To copy a line, you right click on the RX frequency cell, and select copy, then right click on the next line's RX cell, and select paste. Then modify the new line as needed.
Not sure if this is your issue, but once I figured out the "secret" to entering channels, everything went smooth.