Unknown error - 0xA84C (in Endnote X8)

My instittue is very recently updated endnote from x7 to x8.

But after upgrading, I always see unknown error message - 0xA84C when I run EndNote X8 alone.

Also, sometimes the tap for endnote in word is missing from word.

This missing problem is always observed regardless of office version. I found this from office 2010, 2013, & 2016.

To solve this problem, I have to reinstall endnote. 

I tried to several things, but I cannot solve this problem.

How can I fix these problem?

My OS is windows 7 pro 64bit.

and Office is based on version 2013.

Do you have any solutions?? Please help me.