Why a sketch became invisible for path mate?

Hello,

I found a problem selecting a sketch to create a path mate, l don't understand why If a day before I created the same mate with the same sketch! Today I opened the assembly and wanted to continue making this mates but now I can't select the sketch, I can't actually see it on the assembly screen; although I can see it on the design tree as normal, I can edit it and son on... I just cannot use it for this mate anymore! I'm using SW 2010

I need some advices please.

SolidworksAssemblies