When you get the certificate from your browser, the extension format doesnt really matter ( .crt/.cer ... ). You just need to change it to ".der" after downloading it on your computer.The certificate is generated by the cucm so yeah it's self-signed....
Actually i logged on my cucm admin webpage then clicked on the blue part of the url (connexion secured). Then i applied these steps given by someone from cisco:For downloading the new certificate from CUCM and then upload it to CTM
# a.open an IE br...
Problem resolved here.The error message is strange as the problem came from the certificate. I re-downloaded it from my browser on the cucm web page then uploaded it for the test connection page in ctsmanager and that works fine.