If the file downloads or opens successfully, then you may not be affected by this issue.  If you receive a 404 error (page not found), then it is likely that either the viewer files are not present in the expected location or file system permissions are preventing access.  If you receive a 401 (authentication) error, then IIS Authentication settings may be preventing access to the viewer files.

Solution 1:

If you are using a web site other than the default web site, the viewers folder must be copied from the default website to the corresponding location beneath the web site you are using.  A port number other than 80 at the end of your server address (for example, http://yourserver:8080 ) often indicates an alternate website is being used.

In IIS Manager on the server, locate the website where your report web pages are located.  Check the website settings to determine the Physical Path or Home Directory of the website.

Using Windows Explorer, copy the crystalreportviewers13 from beneath the default website (usually C:\inetput\wwwroot) to the corresponding location beneath the root directory of the website you are using.  It is usually safe to copy the entire aspnet_client folder from the root of the default website to the root of the alternate website.

Solution 2:

If more than one numbered folder appears directly beneath aspnet_client\system_web, copy the crystalreportviewers13 folder to each numbered folder where it is not already present.  This will ensure the viewers folder is available regardless of which .NET Framework version is in use.

If the numbered folder found in your page's source code (see "Testing for this issue" above) is not present, manually created the numbered folder beneath the system_web folder and then copy the crystalreportviewers13 folder to the new numbered folder.

Solution 3:

.File system permissions may prevent the browser from reading files from the crystalreportviewers13 directory.  In Windows Explorer on the web server, modify file system permissions for the folder so that the Everyone group has Read access.

Solution 4:

For IIS 7 or later, open IIS Manager and select your web site under Sites.  In the Features panel, open Authentication in the IIS section.  If all authentication methods are disabled, IIS may prevent access to the viewer files.  Enable the Anonymous Authentication, Basic Authentication, and/or Windows Authentication methods.