You can try updating your ACR plug-in to ACR 6.7, but if that doesn’t work because the A77 was released when PS-CS6 was the current version, then you’ll have to upgrade to CS6/ACR7 or use the latest version of the DNG Converter to make DNGs (not PNGs) from the ARWs which can be read in an older version of ACR (= Adobe Camera Raw plug-in for Photoshop).
Buying Lightroom 4 and updating to LR 4.3 is a much cheaper alternative to upgrading to CS6, and from LR, which is essentially the Bridge/ACR adjustment portion of your workflow, can do an Edit in Photoshop (CS5) with LR Adjustments and allow you to finish your edits in Photoshop CS5 if you want.
Personally I mostly use LR and do a few things in PS, nowadays.
I don't know if you mistyped or if you really meant PNG. But converting to DNG is worth considering if you don't want to do any software updating right now. You would still have all the original raw data, but in a new file container, and you would have that file in addition to your original raw file. I usually don't advocate using the DNG converter, except for situations like you are in where your ACR will not support your newer camera. In that case I think it is well worth while. Of course, a better choice would be to either upgrade your Photoshop or else consider getting Lightroom. The raw conversion process version is greatly improved and well worth the investment.
Hi Arthur, This download is for Windows only, is there an iMac version?
Since you’re not the original poster and they asked their question back in Feb 2013, whether a particular link is appropriate depends on a couple things besides the OS:
Is your camera an A77 and are you on CS5? If so, then the answer is to go to the link in Reply #1 and download the Camera Raw 6.7 update which supports the A77 in CS5.
If your camera is not an A77 and/or you’re not using CS5 then the general answer is to use Help / Updates… (or the Mac equivalent) from within PS to get the latest version of ACR available for your PS.
You can use the following link to determine what version of Camera Raw is needed to support your camera: