Getting script error when trying to connect to SSL Remote through Sophos Connect

It's very hard to troubleshoot this as you say.  I've seen it before as I said if they don't have an email address in their user profile in the XG and I've also seen it if they weren't in a group that had access as well.  I'd double check that they are in a group in the XG, and that that group has access and that they also have an email address in their user profile.

thanks for your quick reply.

the user had a generic mail address.

it was in open group - so I created a new local group, put in the user and allowed the group to the ssl vpn profile. no change unfortunately.

Do you use some sort of old browser on the client? 

No, I don't. This is a computer that can successfully connect to the production firewall system SSL VPN with Connect Client.

The usernames on the test system are different than on the live system.

To clarify what happens:

connect client starts,

the pro file has been doubleclicked and the connection appears in SC client

When I connect it, I enter username password, do not get a message that anything is wrong

In eventviewer on firewall I can see the user logging in, like seen here:

SC client brings error: failed to load connection

If I try connect again, I get the .js error message popup

file:///C:/Program%20Files%20(x86)/Sophos/Connect/GUI/js/connections.js

I've seen, that when I download the config manually from the userportal, it has 0kb and not the regular file icon

See: https://community.sophos.com/sophos-xg-firewall/f/recommended-reads/119348/sophos-xg-firewall-troubleshooting-0-byte-ssl-vpn-file

thanks. yes, it's because it's an isolated test environment and the SFOS does not come shipped with the client installers.

Requested file could not be provided. Make sure Pattern Updates are working correctly.
You can find it under 'Backup & Firmware' -> 'Pattern Updates'

Unfortunately, the manual pattern update file does not contain the installers, too.

https://airgap.u2d.sophos.com/sfos_patterns_update.tar

with the help of the link you posted, LuCar Toni I was able to pull the SC installers from the production machine /content/ipsec_1.00/2.1.001, copy that on the test machine, created the links

# ln -s /content/ipsec_1.00/2.1.001/ /content/ipsec

# pwd
/content
# ls ipsec -al
lrwxrwxrwx    1 root     0               27 Mar 10  2021 ipsec -> /content/ipsec_1.00/2.1.001

After a firewall reboot, I could download the files from userportal and then SC could load the config and successfully create the SSL VPN.