INSTALLATION ERROR: Could not load cache Adaptor!

I'm fairly new with opencart. (but I have wide knowledge in coding/developing websites/ etc)
let say I have a domain of www.domain.com with opencart 1.5x
and I've created a subdomain.domain.com
I tried to upload/install new opencart 3.0x onto the subdomain and it return this error:
"Notice: Error: Could not load cache adaptor file session! in /home/domain/public_html/collections/system/library/session.php on line 36Warning: fclose() expects parameter 1 to be resource, boolean given in /home/domain/public_html/collections/system/library/log.php on line 39"

[note that domain isnt exactly named as domain, just for privacy purposes]

any help/replies appreciated. sorry for any mistakes.
Yes, ive tried searching the forum, maybe I'm too pessimistic to search over 1000results or my keyword isnt good enough.
Googling wont help as well.

Well, the only one I found was your Posting on this !
It could eventually be related to an incorrect
.htaccess rewrite
configuration, or then some other rerouting in this file,
leading to the other Shop or so... that's all I can think of.
But it's V.3-specific only, so, there will be more to come on this,
if it's someone else's problem too!
Good Luck !
Ernie