I'm sorry to hear about the issues you're experiencing with your custom modules.
By default a Sitefinity project or module would nto change its behavior unless some external change has been made either to the precompiled code ( a dll has been changed), the configuration files have been modified (under App_Data/Sitefinity/Configuration) either manually or by changing a setting under the Administration backend section, the web.config has been changed, or some of the values in the DB have been modified manually.
In order to make sure we're giving you the best advice we'll need to collect some additional information, namely:
1. Can you paste us the stack trace of the exception you're receiving
2. Is this a custom (created through code) module, or one created using the Module Builder (I see this post has been marked as one for Sitefinity 3.x so if that is indeed the case, please disregard this part of my question)
3. Have there been any of the above described changes to the project configurations, and can you please verify if the module configuration is correct?
Looking forwards to your response.
the Telerik team
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