Can't export mutliple pictures because of full cache space

I am trying to transfer all my edited photos as I want to add a hell of a lot of photos in segments to edit from an event (3000+). I don't want to overload lightroom or my computer so i've split it up into 3 categories. However, when I tried to export roughly 50 photos from lightroom onto a large hard drive, it gave me a warning saying my cache storage is full and the export summary reads only 1/8 of the photos (even less sometimes) made it through to the hard drive. This is really frustrating as I have a client on my back and I don't want to get rid of my precious pictures. I tried clearing my cache but that did nothing useful to the cause. It says that most of it is being used my app and user data... Somebody please explain how I can get my edited photos into a secure spot on my hard drive without them being scattered between exported and not exported!!! The SD card that all of them were taken on is plugged into my computer while I am trying to export them, and there is also a backup for the pictures on my desktop.