I have Classic Quicken for Windows. One day, when starting Quicken, the app started but then showed a blank pop-up window. Trying to close it with the X button, just refreshed the pop-up. Sometimes the pop-up includes the "Please Check Internet Connection and Try Again" text. Using the close option on the left upper corner right-click menu would close the pop-up. However, most actions would cause the pop-up to display again. It seems like at startup, Quicken connects to their online servers and does some kind of validation, but mine was corrupted.
I installed Quicken on another machine, moved the data files from the problem pc to the other machine, loaded Quicken, and did not get the pop-up. Then ran a One Step Update. Did not get the pop-up at any time on this other pc.
Then I loaded Quicken on the problem pc and the problem pop-up no longer displayed. Seems like actions I took on the other pc fixed the problem on the problem pc, I suspect by syncing something on the Quicken server.
[Edited -Readability]