problem with yafaray

Hi every body i am new in blender only 3 month i use yafaray render but I have this problem : when i use yafaray render and during the work suddenly i cant reach to the setting of material and word and other panel becuse the panel change to state show in the attachment image
thanks for your help.

That is a known bug that affects all render systems in Blender 2.6.2, even Cycles. Blender has returned an invalid context to the GUI which causes all the panels to crash.

You can still do a Save at this point. So just save your file, close Blender and re-open and go on.