This is another situation impacted by certificates, and is often seen after the certificate has been changed or replaced on a Group Chat server because it expired or is about to expire.
Basically, when somebody tries to send a file, the file transfer will fail with a message that includes the following:
Could not establish trust relationship for the SSL/TLS secure channel.
There are two places where a certificate needs to be configured in Group Chat. First, the Group Chat Server Configuration tool, and second, the certificate needs to be updated in IIS. In this case, though, the cause of the issue is the certificate in IIS. If the certificate was expired in the Group Chat Server Configuration, then users would not be able to access Group Chat at all.
The easiest way to test if the certificate is misconfigured in IIS is to use the GCWebService.asmx page to test it. You can find the URL for this page pretty easily by using the Group Chat Server Configuration tool. Once in the tool, click on the System Wide icon on the left pane, and then click on the File Repository tab.
Here, you will see the URL. Copy it and past it into a Web browser and see if you get a certificate error or warning. The certificate warning is the behavior you can expect for a certificate misconfiguration in IIS. Thankfully, it is very easy to fix.
Setting the Certificate in IIS is not very difficult at all. All you need to do is follow the basic steps here:
1. Open Internet Information Services (IIS) Manager
2. Expand the server name node
3. Expand the Sites node
4. Click on the Default Web Site node
5. Click on the Bindings link in the Actions pane
7. Use the SSL certificate drop down box and select the proper certificate, click OK and close any other open windows.
8. Restart the Default Web Site and it should be fine.
Try your Web browser again, and you should see results similar to this page (with more links in it).
At this point, file transfers will again work in Group Chat.