If you are using Silk Central 12.0 it is possible to copy and paste some html code in the Custom Information Panel or your Dashboard that causes misbehavior of the UI and this is the cause of the problem.
To resolve this in Silk Central 12.0 execute the SQL statement below directly against your database replacing the project ID with the relevant value for the problem project:
This will delete all of the text from the Custom Panel and enables use of it again. Before doing this ensure that you take a back-up of the database before executing the SQL so you have the ability to roll back in case something goes wrong.
In Silk Central 12.1 we have added an HTML sanitizer that cleans up any pasted HTML code to prevent such problems.