iMovie not seen the System Photo Library
I am new to Photos having recently downloaded Yosemite. Numerous issues but the one I am struggling with is that iMovie cannot see the Photos System Library. Holding the option key while opening Photos reveals only one library which is Photos Library (System Photo Library). Then after opening Photos and going to photos>preferences>general it appears to be correct with pictures>Photos Library showing as the location. The "use as System Photo Library" is greyed out, not sure if thats correct but I think so. Despite all this iMovie will not see any photos with "no media was found" showing. iMovie sees iTunes fine.
Can anyone help?
Mac Pro, OS X Yosemite (10.10.4)