In those cases, when you try to redeploy, you normally get an error message:
Conflict Another transaction by user XXX is already in progressAll you have to do in order to undo the transaction and go back to the initial status is:
1) Open the command line on Windows
2) Navigate to the SDK bin folder on Eclipse. It normally looks something like this:
C:\Program Files\Eclipse\plugins\com.google.appengine.eclipse.sdkbundle_1.8.7\appengine-java-sdk-1.8.7\bin>
3) Type the following command, where the last parameter is the absolute path to the war folder of your GAE's project:
appcfg rollback C:\Users\Arturo\workspace\Dialective\war4) Use your Google App Engine credentials when requested. And that's it!