The RadCaptcha displays grey image when the CaptchaImage cannot be found. This could be a result of:
- Using the captcha in a website with enabled load balancing. This help article
contains more information about the scenario;
- Clearing the Cache/Session of your project. The CaptchaImage is stored in the Cache by default or in the Session if the control is configured as described in the help article, linked above. If the storage location used by the captcha is cleared, the image will not be displayed.
the Telerik team
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