I have a similar problem to the ones listed here and here.
I am getting an INSTALL_FAILED_DEXOPT error every time I try to install my app on my Motorola Xoom.
<I suggest running Eclipse and viewing LogCat output to see what the actual error message is. I was getting this error and it was because my device was low on storage and it was failing to unzip the APK. I believe there are multiple reasons that this error can be triggered and uninstalling or clearing user data may be unnecessary.