The Login failed for user
error may occur if the user does not have proper permissions to access the database or that the identity that is managing the application pool for the site does not exist in the SQL Server instance. The problem may also occur if the worker process of IIS is not able to authenticate to the SQL instance at some point, or the identity used for logging to the site is not correct.
Can you please let me know more details about the issue and when exactly it reproduces? Does the issue appear each time when you try to login to the Sitefinity backend or it only reproduces when you try to access the page where you have dropped your custom widget?
As far as I understand, you have created a user control in your Sitefinity project in Visual Studio and have added a GridView control in the markup. Can you please let me know what is the data you would like to bind to the GridView? How do you get the data in the code behind and how do you bind the data to the GridView?
Can you please let me know how you have registered the widget in the Toolboxes, so that you can drop the widget on a Sitefinity page? You can easily register widgets with a couple of clicks using Thunder. Please refer to the following article
for more details on this. Can you please try registering the widget using Thunder and let me know about the results?
It would be grate help if you can record a video demonstrating the exact steps on your side and how the issue is reproduced. This way I will be able to get better picture of the problem.
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