This can occur if the directory you are trying to write to does not exist, or if you don't have write access to that directory. While you can "write" to files which don't previously exist (MATLAB will create them), the directory does need to exist beforehand.
This can also happen in some situations where the user which starts the Excel is a system user. Excel expects the existence of the Desktop directory. To enable the command to work try the following:
For x64 processes create the following folder:
C:\Windows\SysWOW64\config\systemprofile\Desktop
For x86 processes create the following folder:
C:\Windows\System32\config\systemprofile\Desktop
