This plugin won't compile for AMXX 0.20, and the web compiler won't give any errormessages, so I can't tell you what the problem is
Edit: Actually, it's due to the 20-character limit on variable names.
If you change every instance of desired_velocity_towards_A to d_velocity_towards_A the plugin will compile fine.
I included the fixed version in case anyone wants it.
(Edit: It seems to have been fixed now, so I removed the version I posted)