Cannot deactivate Adobe CS5 Web Premium

there's no longer support for cs5.

adobe connection errors are common and are not related to whether you're connected to the internet.  they're related to connecting to adobe's secure servers.

if you have a non-current os, your default browser must support tls 1.2, https://helpx.adobe.com/x-productkb/multi/eol-tls-support.html

to test your default browser's tls you can use , https://clienttest.ssllabs.com:8443/ssltest/viewMyClient.html

otherwise, confirm that you can connect to the secure adobe servers by reading, http://helpx.adobe.com/x-productkb/policy-pricing/activation-network-issues.html

do you see both logos after clicking "link"?

if you can and still see a connection error try these steps, https://helpx.adobe.com/download-install/kb/common-network-connectivity-issues.html

if those all fail, white list the adobe network endpoints, https://helpx.adobe.com/enterprise/kb/network-endpoints.html

or, if you’re trying to activate a perpetual license, you can try offline activation by disconnecting your computer from the internet, starting activation and using https://aoes-stage.licensingstack.com/aoes/aoes/v1/imsauthstatus