Automatic upgrade fails

I just tried upgrading the blog I have installed under a subdomain/subdirectory of my domain to RC1 and it didn’t work. I also had to upgrade to beta2 and beta3 manually.

The automatic upgrade of the main blog (same domain but no subdomain) worked fine to beta3 and RC1 (upgrading to beta2 didn’t work).

Does this have anything to do with the fact that it’s running on a subdomain? Is there any way to fix it? The error I get is this one:

Downloading update from https://www.ads-software.com/nightly-builds/wordpress-latest.zip

Unpacking the core update

Fatal error: Cannot redeclare class pclzip in /home/content/e/a/r/earthtobella/html/run/wp-admin/includes/class-pclzip.php on line 171

Thanks for your help.