Problems installing all versions-2.1.9, 2.1.5, 1.10.9

I reviewed the support threads regarding the known problems with upgrading, and was unable to resolve my problem. Please read my entire attempts before responding.

After upgrading WordPress and then upgrading to v2.1.9, I also had the blank white screen with the following info in my Dashboard:
“All-in-One Even Calendar: CSS compilation failed because you do not have enough free memory (a minimum of 24M is needed. Your calendar will not render or function properly without CSS.”

These are the steps I took:

1. I disabled the plug-in and contacted my webhost who informed me to use my wp-config file to increase memory to 64M, which I did. This did not resolve the problem. I then also tried the switching themes, which did not do anything either. (I attempted and tried both of these several times).

2. I downloaded v2.1.5 and uploaded via FTP. When I activated v2.1.5, I had the following error and no other website display:
“Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 71 bytes) in /htdocs/www/wp-content/plugins/all-in-one-event-calendar/vendor/lessphp/lessc.inc.php on line 2510”

3. I again tried to alter the memory in my wp-config file, which did not work.

4. I removed v2.1.5 and re-uploaded the previous version I was using, v1.10.9. This version will not activate at all.

My client depends on the calendar and several of the website pages have the widget in the sidebar. I was hoping to at least restore the previous version so that they will not be without the calendar until issues are resolved, but this has not worked.

Thank you.

https://wordpress.org/plugins/all-in-one-event-calendar/