Hi there!
There are no known issues with Cassini Explorer installation on Windows 7. It's possible that Explorer got installed but 7756 is used. You can run "netstat -na | more" command to see which ports are taken, but it's only useful if you are sure that Cassini Explorer did not get installed. If you know it didn't get installed, please check Event Viewer (Application) - it is likely to have an error entry with information on installation failure(s). Unfortunately, you will need to have access to the machine in order to troubleshoot the issue.
Please let us know whether this information was helpful.
Best regards,
UltiDev Team.
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