romolo Hi
You may also check for troubleshooting steps here :
1) Some steps here to try here might be of help
2) You can find the actual php memory available by trying the steps outlined here in redirection link and try to increase memory_limit by step outlined here
here can be a discrepancy between the PHP memory listed as available in the system information and the error. To confirm the actual memory available, read the following link and run the small file included in the page entitled Are you getting your fair share of PHP memory?
3) As also suggested earlier, You may also try and assign Default Joomla Template to some test page on the similar hosting environment to see if issue persists related to session getting timed out
Strangely, I am getting "session expired" message while logging for the first time in admin panel. ref: screenshot
If the hosting provider is unable to allocate much needed actual memory, You may wish to go in for option-2 as suggested in forum thread :
Option 2
Moving to a web hosting company with more generous resource limits might be a reasonable solution too.