I just tried to open it and got the following error from Adobe.
My gut feeling is that something changed either with the tool you use to create the PDF, or with Adobe. Frankly, this likely is because the Adobe "standard" is now (and perhaps all along), somehow not being completely followed and at some point - usually due to an update to Adobe, the reader said, "nope, I can't deal with this any more".
It's similar in fact to what happens with wireless routers and how they will work fine with one phone but then as of the sudden a new phone can't connect. It's not because the router has failed, our that the phone is the cause. It's usually because the " standard " wasn't being followed 100% with the earlier router firmwares, and the newer phone is adhering more closely to that standard.
This is often due to software (*and hardware), manufacturers trying to avoid paying the Adobe licensing fees to utilize the actual PDF creation code, and instead create a quasi mock-up of code that will "essentially" create a "pseudo-PDF". Adobe knows these packages exist and they will often try to tweak their code to both remain completely compatible with their own standard, while essentially "breaking" the third-party non-licensed applications that try to "ride on the PDF train".
This may not be the cause, but the sudden change from working to not, and the error I got cause me to believe this is the cause. If PDF files created by "licensed" PDF creation software, but will not open those with your application, I would suspect the application to be the fault.