coelogyne massangeana not happy, what did I do wrong?

[playtime8978]

I checked my plants last night at light turn off time and all were happy just a few were in need of water which they have just got, all the plants looked healthy. This afternoon when I got home from the hospital this was not the case my Coelogyne massangeana had a very yellow and brown leaf. When I got the plant about 10 days - 2 weeks ago this leaf had been cut across and the very edge which was cut was browned slightly, it has done well since, any way back to the point the leaf was very yellow and browning had moved down the leaf. I cut the leaf off using a sterilised blade and dusted the top of the pseudobulb where I cut with cinnamon. The plant had slight web on the under side of one of the leaves yesterday so my husband sprayed it with an insecticide and it got left in the kitchen for the afternoon there were no signs of any infestations on it other than that one area of webbing on the underside of the leaf all the other leaves ok healthy to me and seem ok. I was wondering if anyone could tell me what has happened. It seems to have happened too fast to be normal leaf die off. All suggestions and ideas most welcome I have removed it from the other orchids and it is currently in disgrace in the kitchen! I appologise in advance for the quality of my photos I am very unsteady today.