Not much on troubleshooting usually turn to Google once it spits out an error message. Here is a breakdown of what I had to do when I originally started using impactor:
-Make sure iTunes installed/updated, not sure about everyone else but I also have to leave it open in background.
-Make sure using newest impactor, I currently have 0.9.51, couldn't ever get 0.9.45 to work.
-Make sure you have gone to your Apple account, and under security you have created an app specific password this is the password you must use with impactor(might want to create a new apple account too so you're not using your main one for sideloading).
-I am on Win 7 X64. Also have this working on Win 8.1. All 3 phones are iPhone 6+'s. One with 12.1.1, and 2 with 12.1.2
Pretty sure that's all it took for it to work. Never could get .45 to work for me but others have had success. Haven't checked last couple weeks but I think .51 is still the newest out there. Hope this is of some help. If getting an error message during the loading process just google the message you'll find info out there on all the messages it generates.
