I have to downgrade my C20 from 5.x to 3.x because in 4+ version I has issues with video-freeze during 5-7 minute of a call when I connects to Sony codec (G50). When I had 3.x version it worked fine. My devices were shipped with 3.0 version.
When I try to upload old firmware (3.x) using codec’s web interface it shows me “Corrupt software-package uploaded.” I downloaded all 3.x firmware files – each file had the same result. How I can to downgrade to 3.x?
Have you try upgrading software by directly uploading software on EX90 by using SCP instead of upgrading from Web GUI?
If you are using Windows, then WinSCP is probably most friendly application for uploading software to EX90.
If you are using MAC, there are several similar application (fireftp, Cyberduck, etc.) and you may also create WinSCP.app by using WineBottler (to use WinSCP on MAC).
BTW which TC3.x software are you trying to downgrade on your EX90?
Please note if you have newer HW (system ship out from Cisco with TC4.0.4 or newer version) may not compatible with old TC3.x software “except” TC3.1.4 (additional information is available on TC3 release note).