Unity XL V8.0 on Windows 7 64 bit must re-register the msxml4.dll file in the Windows registry.
This dll is located in the \ windows \ SysWOW64 directory.
To register the file do below steps :-
Click the Start Menu tab in windows 7
Type regsvr32 c: \ windows \ SysWOW64 \ msxml4.dll
Click the Start Menu tab in windows 7
Type regsvr32 c: \ windows \ SysWOW64 \ msxml4.dll
Click OK to register dll file and this will solve the problem.