I am having the same problem with my note. It started since i added the dropbox app (which i love) and associated my phone with my online account. the device has done the same thing as yours above and does not allow me to open the gallery.
i can still take photos. so there isn't really a space problem. i can still view videos from the video library, so it cant be a memory issue really.
looking at settings, storage, my device memory is 1.97 Gigabytes my USB storage 11.07 Gigabytes and SD card has 14.27 Gigabyte free. However the applications shows 115 Gigabytes of memory is used. If i tap on applications from there i do not see any sign of this memory being on one of the applications in the list under the all, running, on sd card or downloaded tabs.
i need help as i am sure its a glitch but cant find any resources to help me!