I have an existing project tied to a Sandbox org. When I created the project, I received errors "Sequence contains no elements" when trying to pull down about half of the types (triggers, layouts, apex classes, etc.). So, I was able to create a project successfully by selecting only Apex Classes.
I then right click on the project in the solution explorer and select "Project Metada Components" and add just one more group, i.e. Layouts. When I click on an additional group, the window displays the message that I must pull from salesforce when adding new components. OK, so I cancel, right click the project and Pull from Salesforce and after a few seconds, the IDE says I have all the most recent files.
I then try to add new metadata components and still get the message that I must Pull from Salesforce to add new objects. When I click continue, I get the error message "We could not get Metadata", "Please try again later".
I have submitted a bug report (unique ID ED2363D9A558A4A8B8CC4421E742223C) through the IDE but wanted to include here as well for others searching.