LEED sample forms not opening.

Yes, the adobe forms are a known issue. However, at this point most (all?) LEED Online forms have been upgraded to the HTML version, so there shouldn't be a need to use them at this point.   If you do need to use a sample form .e.g for attempting a credit from another rating system as an innovation point, I recommend saving it to your computer and opening with your PDF reader rather than trying to view in the browser. And then you may want to capture a screenshot of the completed form rather than saving the PDF. 

Hi Marine, Are you actually doing a Precertification? LEED projects all start with that scenario when you register them. Most of us are not doing that and go to the Timelines tab to change the project to either split or combined submittal. Once you do that the credits and forms you are seeing will change. Could that be part of your issue?

Like Michelle said, the USGBC is "encouraging" buying that Pre-Certification extra and it comes up on all projects until you go into "timeline" to change it.  HOWEVER, that may have nothing to do with your issue. Emily was correct. Generally, the forms don't open to preview, or directly from the site, on most computers. Try downloading the forms from the LEED resources page, where it sounds like you were, and only try to open them afterwards from your files. You need to have Adobe Reader (free) 11 or DC to open them. Arobat also works but since I don't have it, I don't know the versions.