The Error 105 (or -105) when attempting to make a backup of your iPhone via Decipher TextMessage is usually indicative of a drive space issue on the iPhone, so let's start by checking there.
Open the Settings app on your iPhone, and go to General > iPhone Storage.
At the top, what does it say for X GB of Y GB Used? If the phone is at absolutely full, this screen may be helpful in finding an app with a lot of data that could be freed up. You don't need a lot of space to make a backup, but iOS does create a few files while it's backing up (information about the backup, and the list of files in the backup) which can sometimes take 200MB or so.
After freeing up a bit of space on your iPhone then try the backup again.
If it is still not working for you, please use that contact support button in the backup window within the program so the new error log fills in for us to review. If the backup completes there, then run Decipher TextMessage and it will read in the iTunes/Finder backup and you do not need to backup in Decipher TextMessage.
Or if you still have troubles, please contact us via our Decipher Tools Support page and we will write you back to assist!