AppDNA places a lock on critical tasks so that another user cannot delete or modify the data while an analysis is being performed. Generally, AppDNA releases the locks at the end of the task. However, in certain circumstances (such as a restarting the server) this does not happen. You then need to release the locks manually.
The Tasks screen shows the status of all of the imports and analyses being processed by all of the AppDNA clients connected to the same AppDNA web site.