Cannot delete or deactivate plugin

I need to deactivate all plugins to solve another problem, but no matter how many times I click “deactivate” or “delete”, the WP Missed Schedule plugin (version 2013.0730.7777) remains unchanged.

This happens whether I try to deactivate it on its own, or whether I do it in bulk along with all other plugins. Obviously I cannot delete it either, since I cannot deactivate it and you cannot delete an activated plugin

Here’s the details of the system I’m running:

Mem: WP 40M Usage 43% 27.72M Limit 64M *

Server: OS Linux Software Apache Version 32Bit
System: PHP 5.3.2-1ubuntu4.21 SQL 5.1.70 Build 5.1.70-0ubuntu0.10.04.1
WordPress: VER 3.6.1 Max Post 100M Max Upload 100M
Debug: State 0 Display 1 Log 0 Script 0 Deprecated 8192

SQL Uptime: 18 days, 20 hours, 31 minutes, 43 seconds

Default Theme: twentythirteen (since wp-3.0)
Allow DB Repair: 0 (since wp-2.9)
Auto-Save: 0 Interval 60 seconds (since wp-2.5)
WP (Hyper – Super – W3 Total) Cache: 0 (since wp-2.6)
Magpie RSS Cache: 0 Age 0 seconds (since wp-1.5)
Post Revisions: 5 (since wp-2.6)
Trash: 0 Empity 30 days (since wp-2.9) Media 0 (wp-3.0?)

http://wordpress.org/plugins/wp-missed-schedule/