Error executing an Alter Table command to drop a foreign constraint: "Object reference not set to (4223893)

Executing an Alter Table command from Object Explorer results in the following error.

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Exception Information
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Exception: System.NullReferenceException
Message : Object reference not set to an instance of an object.
Stack Trace:
at Quest.Toad.Editor.EditorForm.refreshBreakpoints()
at Quest.Toad.Editor.EditorForm.RefreshCodeTrls()
at Quest.Toad.Editor.EditorForm.Parse(Boolean
processParserMessages)
at Quest.Toad.Editor.EditorForm.DoExecuteSqlScript()
at Quest.Toad.Editor.EditorForm.ExecuteSqlScript()

RESOLUTION:

1. In Toad, select Help | About.
2. Click on Application Data Directory link. This will open the directory where the User Files are stored.
3. Close Toad.
4. Rename the Toad for SQL Server 5.x folder to Toad for SQL Server 5.x_old.
5. Open Toad.