我在stata中安装synth package，可是总是提示：

-------------------------------------------------------------------------------
package installation
-------------------------------------------------------------------------------
package name:  synth.pkg
        from:  http://www.mit.edu/~jhainm/Synth/
checking synth consistency and verifying not already installed...
I/O error
could not copy http://www.mit.edu/~jhainm/Synth/synth_ll.ado
(no action taken)
r(691);
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(click here to return to the previous screen)
这样的错误，点击r（691）查看，说是
  error . . . . . . . . . . . . . . . . . . . . . . . .  Return code 691
        I/O error;
        A filesystem error occurred during input or output.  This
        typically indicates a hardware or operating system failure,
        although it is possible that the disk was merely full and
        this state was misinterpreted as an I/O error.
本人新手，求高手指点！