When trying to insert a block, the insert block window does not appear. Intead a thumbnail of the previously used block is displayed in the lower left corner of my screen. From this point, I can't make any changes in AutoCAD. I can only press ESC to cancel inserting a block of which AutoCAD resumes to normal operation.
2. Then use an uninstall script supplied with the application. It cleans up additional files that are not in the "/Application" folder. To run it, launch a terminal window and run: ~/Library/Application\ Support/Autodesk/local/AutoCAD\ LT\ 2012/R18.2/enu/Uninstall/Uninstall_AutoCAD_LT.sh
I have reinstalled AutoCAD, and it works again. However, I tried the steps you outlined running the command in Terminal. The only feedback I get is that the folder or directory doesn't exist, even though I can find it through Finder. Instead I had to search for the .plist files and delete them myself. After getting AutoCAD to work the first time, a week later, the same issue occured. It appears to happen at random, i.e., I opened up a project the first time that day and I couldn't insert a block. Instead of reinstalling AutoCAD, I just deleted the plist files and it works again. No issues have occured now for over a week.
It's a strange issue. Thankfully the temporary fix is easy yet annoying.