Activation straight after install returns this error, but activating after this from the installed plugins page does work.
I think it’s because there are actually three plugins inside the package… The main plugin and the two drop-in files in the drop-ins/ directory. The “Activate plugin” link after installation tries to activate one of the two drop-in plugins that do not have a valid header.
UPDATE: I tested by removing and reinstalling and indeed, the Network Activate (I’m on a multisite) link tries to activate wp-spider-cache/drop-ins/advanced-cache.php instead of wp-spider-cache/wp-spider-cache.php
I suppose a fix could be to remove the partial plugin headers from the drop-in files, as they don’t need plugin headers at all.
I can confirm I also have this error, when installing via WP admin.
Using WP 4.5.2
