License file corrupted, though just downloaded

Unfortunately Avast Internet Security is getting more and more frustrating with Windows 8.1.

I have a license for Avast Internet Security valid until 23 Dec 2015.

After the most recent update, the PC has become slow and choppy. Avast consumes 33% of CPU. So I uninstall it, reboot and launch Avast Free. I try to upload the license file (which I have on my Desktop) but the answer is: file corrupted or modified. I have never edited it, I know it wouldn’t work anymore.

So I login on Avast website, successfully. My license is there. I download a new file. No way: file corrupted or modified. I try to connect to my Avast account from Avast Internet Security. Result: cannot connect your device to your account.

I cannot remember such a sequence of failed attempts in my PC experience. Should I look for a new antivirus?

avast support https://support.avast.com > submit a support ticket

I had tried, but I could not login for some unknown reason.

Nonetheless, the problem is fixed now, after rebooting my PC a second time.