The GH4 requires ACR 8.5, so the AAM is correct: There have been no more updates to CS5 or CS5.5 once CS6/ACR 7.x came out, and we're up to CC 2014, now, soon to be CC 2015, so you either have to upgrade to a current version of PS or use the free DNG Converter 8.5 or newer to create DNGs out of your RW2 files, then those DNGs will open in your older plug-in.
For reference, here are the versions of ACR that are needed for each camera model Adobe supports:
And here are the versions of ACR that work with each Adobe software program:
Other than the free DNG Converter, your cheapest option is the CC Photography Plan for US$10/month (a different amount in Australia) that includes both the latest PS-CC and Lightroom as long as you keep paying:
Many thanks for your help. I want to avoid paying monthly for the Cloud - but would be happy to upgrade to CS6. Though from what you say CS6 may only support ACR 7.
Do you know if it is possible to just upgrade Adobe Bridge and Photoshop from CS5.5 to CS6? In this way i should be able to view the thumbnails for the RW2 files and the MP4's - and to open the RW2 files in Photoshop. If i just upgraded Bridge and Photoshop would i still be able to use Premiere, Audition, AfterEffects as before? Currently i can drop the MP4's into Premiere and they work fine. Just can not view them in Bridge.
CS6 is still being sold by Adobe as their one non-subscription offering, so they relaxed their rule about stopping with ACR 7.x and version and ACR 9 can be hosted with CS6, but the updates are only for new cameras, and you cannot use the new CC features like HDR and Panorama of ACR 9, the new auto-perspective-correction (Upright) modes of ACR 8, nor the soon-to-be-released Dehaze filter in ACR 9.1 for CC subscribers only, and the OS requirements for ACR 9 may be newer than those for CS6 so check those to make sure your computer is new enough.
Finally, an upgrade from CS5 to CS6 costs $200 for regular and $400 for extended, so 20 months and 40 months respectively.
You can buy it, here:
Or search adobe.com for (Photoshop cs6) click Photoshop CS6 in the search results, then click Buy CS6 at the top-left menu, then click Buy next to PS-CS6 or PS-CS6 Extended and switch it to Upgrade.