InfoPath Dev

I have put together a very complicated infopath form that up until yesterday worked just fine as a web browser enabled form. Yesterday afternoon and today (after removing the fields I added/modified) I'm getting the above error. I did some research online for troubleshooting but can't figure it out! I saw that there might be an issue with using a filtered lookup from a list in SharePoint, on repeated sections but I removed them and still get the error. Any help/suggestions, etc. would be greatly appreciated!

Is this being published to Office 365? or to an internal server? I usually just save a copy of the form, publish it to a new library, then start pulling things out to track down the issue.

Hilary, It's being published to a SharePoint 2013 Library. I tried doing just that, created a new library and took out the added fields and it still doesn't work. What does this error really mean? Thanks for your help, I really don't want to start over! Cheri

Often what it means is that the Sandbox Service is timing out trying to review the form for compatibility. Sometimes running Fiddler while running the design checker will give a better error message (in Fiddler), but not always. How quickly does the message pop up? You have the form set to verify on the server and have the server address entered?

Honestly I'm not sure what Fiddler is. What happens is I click on Quick Publish because I have the publish options already set up and it goes through the process and then gives me this error: "The form template has been published to the server but it can only be opened in the InfoPath Filler because it contains features that are not compatible with Web browsers. To fix this problem, close this dialog and review the errors in the Design Checker task pane." Then I click OK and in the Design Checker it give me the error I mention in the subject line. My users are on iPads and thus don't have InfoPath filler. Actually neither do their laptops. And like I said up until a couple of days ago, all was working fine.

What I am suggesting is that you look under the Form Options, and check Compatibility. Enter the server URL for verifying and go to Design Checker and hit refresh. Fiddler is a tool that can be used to view web traffic on your machine - sometimes the errors returned don't make it all the way back to InfoPath. If this were my form, I'd save a copy then start removing things to see if I can get it to publish again and to help track down the problem - I usually start by removing one view at a time. Again, save a copy, as this is destructive.