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I have just seen that LR is Adobe's first 64-bit app, and that one has to turn it one.
I have had a look for this button, even in help, but could not find it.
Could someone point me to where please?
Yep... browse to the application in Finder. Click once on the application and press CMD-I to bring up the info window (or right-click and select Get Info). Uncheck "Open In 32 Bit Mode" and from that point forward, Lightroom 2 will run in 64 Bit Mode. You will need to close and restart Lightroom for this change to take effect. To get it back, just re-check "Open In 32 Bit Mode."