Oddly, my client’s host only provides 48M of memory. I asked them to increase it but it’s a no-go without changing hosting package at 4x the cost. However, they temporarily increased it to 64M just for testing purposes and in that time I was able to install & activate both Jupiter and Connections without any issue. They have now decreased it back to 48M but the error message has not come back! So fingers crossed it stays that way. If not, I’ll move the site to a different host.
Thanks for your help!