I had the same issue. I tried on 3 different computers and even played around with the dates to try and make SOMETHING work. I have no gaps in history and everything is in order from the most current. I read where some people had trouble and resolved it by putting the current date as the end date instead of selecting "ongoing". This, however, didn't work for me. I was unable to save it. The print option was disabled so I couldn't even print it. They updated the form sometime in January and I hoped they had fixed all the bugs but I AM STILL having the same issue. Very frustrating. The update did however enable me to save and print the form. So I ended up mailing it in as I already had my police clearance anyways. If they request that I upload the Schedule A (as I have seen that they are doing even if you mail a hardcopy), I will make one last attempt to validate. If it won't validate, I will just have to upload it unvalidated. I'm kind of out of options at this point. I can't make it do something that it won't.
Good luck