seguisym.ttf is in the installation files
search for it in your c:\windows\winsxs folder, I found it in:
G:\Windows\WinSxS\x86_microsoft-windows-font-truetype-segoeui_31bf3856ad364e35_6.2.8400.0_none_59e76c75ea4463da
Explorer should open the sxs container file, and a right-click should allow you to install the ttf.
Beyond that sfc /scannow should fix it, I think