Fatal error: Class 'WPMinifyCommon' not found in C:\...wp\wp-content\plugins\wp-minify\wp-minify.php on line 50
The class is there in the common.php
This is sometimes to do with the order of the definitions of the classes (php 5 fussier than earlier versions). I tried moving the require_once statement up to earlier in the file and then tried to activate. No go.
Then cut and pasted the contents of common.php into the main file between the end of the other class and the next php statements.
Save, reactivate... now it is happy!