Have a look at this Troubleshoot video issues in Lightroom 4
When you say it hangs when swapping between catalog how do you mean because it should tell you it will need to shut down and restart lightroom.
Thanks for the link but that link mainly relates to Windows and I've already tried all the various ways of importing files. I even copied the contents of the SD card to my hard drive and tried to import it from there. It does not work. I've tried just Adding to the catalogue rather than using a Copy, it doesn't work. The videos themselves are fine and even the ones that used to work in LR4 now don't work in LR5.
The swapping I referred to was when you are in one Catalogue and you switch to another. With all the previous version of LR it prompted you to do a backup first and then would quit and reload itself with the catalogue you're switching to. I have to force quit the app, then it will load the catalogue I want. I've sidestepped this bug by having LR ask me which Catalogue I want to use on startup so I don't need to swap.
So not help from this forum nor any ideas from Adobe. Useless, typical crap support from Adobe. I'll head off to Pirate Bay see if I can find something there, much better value for money.