"Cannot run this program" message

We updated our computers earlier this week, and since doing so a couple of staff have started to get the message below when using the desktop version of Outlook;

"Cannot display this folder. There is not enough memory to run this programme. Quit one or more programs and then try again"

This comes up when there are no other programs open to close down. I have checked to make sure that 'Download Public Folder Favourites' is not checked as advised online. I have 92.3Gb of 99GB free space in mailbox settings