Two possible answers:
There can be a few different things that would affect this. In this instance it was this line (below) in the web/web.config that was commented out. They would needs to be ensure it is uncommented.
<handlers> <add name="CrystalImageHandler.aspx_GET" verb="GET" path="CrystalImageHandler.aspx" type="CrystalDecisions.Web.CrystalImageHandler, CrystalDecisions.Web, Version=13.0.3500.0, Culture=neutral, PublicKeyToken=692fbea5521e1304" preCondition="integratedMode" /> </handlers>
Other things to check would be the version of CR running on your server. Try downloading and reinstalling CR Service Pack 25 Version 13.0.25 or later.