I have seen this issue in the past and it is almost always that the entity has been corrupted and needs to be removed or otherwise repaired of the issue on the back end. It is not really recommended to make backend non gui chnages so I would suggest that you get with your ALM specific support team to address it.
Note what actions had you performed that lead to this error. Note what were you doing and how were you entering this data, as if a screen shot (using the screen capture tool, or by using a third party screen shot/screen capture tool and then pasting the image into the comments or what was occurring because we see issues using certain actions that can lead to corrupted comments sections and the entity being inaccessible)? As long as a defect in error is highlighted each time the defect module is entered the issue will repeat and lock the client. You may have to get out of the error and change the view type and then exit the module and the next time you enter the module the error shouldn't occur (as it will always occur so long as the focus on a defect in error is present.
Hope this helps, but you may need to engage your ALM support team to insure nothing is damaged further,