Hi Paul, welcome to the forums!
Couple of things it could be, but first off I'd have a look at the Autoplay settings for Pictures and/or Mixed Content (i.e. what does the operating system think it should do when a new volume with Pictures or Mixed Content is detected).
Go to Control Panel, then click on Autoplay - in the dialog box that pops up look down the list to find Pictures and see what the action is associated with it. If it is "Import Photos Using Adobe Photoshop Lightroom 1.4" then that's the problem. To fix, click the down arrow at the right-hand end of the line and some further options will be displayed. One of them may even be the option to use Lightroom 2.6, if so select it. If that option is NOT there, you could simply choose "Take no Action" which would mean you have to start LR yourself when you insert a picture card.
Repeat if needed for "Mixed Content" further down the list....
If that's NOT the answer, come back and we can explore some other things....
