"Installation Failed: Can't install the software because it is not currently available from the Software Update server."

After I have updated my iPhone, I have to install a software update that is required to connect my iPhone to my iMac using iTunes. It sometimes happens but however, unlike the other times, I can't seem to install it. Before this happened, I was able to download and install it, but when I connected it again, it asks me to download it again. Then afterwards, it wouldn't let me because it isn't available from the Software Update server. Can someone tell me how I can fix this so that I could import my files to my iMac?

Also I did check an Apple Support article about it, but trying them doesn't work at all. That's why I came here to ask.