Can't install DP2 - "Couldn’t communicate with a helper application"

While trying to update to DP2, I keep getting this error from the App store: An error has occured: Couldn’t communicate with a helper application"

Anyone has a hint on what to do? What could it be and how to get around it?
Currently I am again downloading DP1 to try to reinstall and start from there, but if you have any workaround, please come forward.

Many thanks to you all.

redetection said:

there is command line utility called softwareupdate, use it for this time.

Code:

$ softwareupdate --install --all

Click to expand...

Thanks very very much!