Rename Sheet - Macro Error

For some reason, a certain part of my Rename Sheet macro keeps getting a "Compile Error". This is inconsistent - the macro works perfectly on my laptop but not on others.

Here's a screenshot of the error. (The "Left$" is where we're having the issue)
Macro Error.jpg

Can anyone figure out why? Any help is appreciated!!

Hi xlbiznes! Thanks for the advice.

Turns out it was because someone used a newer version of Excel 2013 and referenced Outlook 15.0 (while I have Outlook 14.0).