Re: Have downloaded new Lightroom 5.4 from CC. When trying to launch am getting following error message and then Lightroom crashes: "an error occurred when attempting to change modules". Can't find a thread which relates to this error message.

I would suggest uninstalling LR

Then log-out of Creative Cloud

Shut down your computer

Re-start your computer

Log-in to Creative Cloud with your Adobe ID (email & password)

Wait for apps to be refreshed and then scroll down the list to Lightroom

Click install button