No More Custom Number Format ERROR

I am working with a model in which I am converting to a
current scenerio. When I go into a specific cell to
change the link it gives me a error that reads "No more
custom number formats can be added." I don't think this
has anything to do with my links, but the only work around
I can see is to plug in the number. I don't want to do
that due to it being a model that updates its self. Has
anyone had experience with this error message. Oh and It
totally shuts me out of Excel.

Thanks for your replys