My first guess would be the memory assigned to PHP has been exhausted. I question that a little because deactivating other plugins would/should improve the situation.
What is the memory settings now? You can find this on the Connections : Dashboard on the System widget. There will be two numbers, one for the setting and the other for usage.
If those two numbers are somewhat close, try increasing the memory. Here’s and excellent blog post which includes several methods. With method that will work for you depends on your host, so I suggest starting at the top and working your way down the list until the issue is hopefully resolved.
Oh, please make sure you’ve updated to Connections to the newly released 8.1.2 version.
Hope that helps!