The other day I filled up with gas and when I went to leave the station I jumped on the bike which was in first gear, took it off the centre stand, turned the key on, moved the kill switch to the center position and pushed the starter button. Nothing happened. When I put the bike in neutral the bike started fine. Most of the time I put the bike in neutral while on the centre stand, start the bike and let it warm up. I cannot recall specifically starting the bike, with the clutch in, while in gear for a while but I am sure I have done it.

What could have broken that would not allow me to start the bike in gear, with the clutch pulled in, and allow me to start in neutral?

Thanks in advance

There is a small switch associated with the clutch lever that when you pull the lever in it allows power to the starter relay.
The switch is on the small cable that goes into the lever assembly just to the rear of the main operating cable.
They are noted for getting stiff and not working properly with age, you can usually use some WD40 or CRC and get them going again or they are still available new.
You will be best to remove the clutch lever and then you can get at the tiny plunger, which is in the space occupied by the lever, to work the plunger and apply WD40. If you need to remove it a 11mm or 7/16in long socket is needed.
Only attempt to remove it if you need to replace it as they can be very difficult and often need to snip the cable to get the socket on them. Sometimes a pair of long nosed pliers will get it out and that is worth trying first.

This is how I removed my switch.

 https://www.k100-forum.com/t6270-a-spanner-to-undo-the-handlebar-clutch-switch

Paul.

Thanks RicK. I pulled in the clutch and held it with a clamp. I could see the plunger so I pushed it with a screw driver to see if I could free it up. I sprayed a bit of WD40 and again pushed it with the screw driver. I was able to get a small needle nose plier in to pull the plunger. It seemed to be freed up so while the clutch lever was clamped I tried to start the bike while in first gear. It started!! 

Thinking me problem was solved I unclamped the clutch lever and put my tools away. I then pulled the clutch and tried to start the bike again. No start!! 

Perhaps I need to work the plunger with a bit more WD40, or perhaps the switch is in need of replacing. If in need of replacement I guess I will need to fabricate a removal tool (Thanks Paul)

Thoughts.