Amy - thanks for the reply, but I was able to figure out the issue.
For anyone else trying to put a VisualForce page into an iFrame and the VisualForce page is coming up black here is a potential solution.
Salesforce has a feature called Clickjack Protection which I believe is designed to prevent malicious links being displayed through an iFrame to Salesforce users. To access Clickjack Protection go to Setup -> Security Controls -> Session Sharing -> Clickjack Protection.
Salesforce requires the first two settings be Enabled by default. However, it is the second two settings that, if Enabled, can cause issues with putting a VisualForce page into an iFrame within a Skuid Template.
In my case the last option was Enabled and the LinkedIn Sales Navigator for Salesforce VisualForce page had showHeader=“false”, so it was getting blocked. Turning off this feature fixed the issue and the iFrame worked as expected.
Hopefully this helps anyone else running into this issue in the future.
Andrew
