The error your experiencing only occurs if the app receives an invalid reply or no reply to a command. Furthermore, I try these commands three times on failure. Based on these findings, I suspect the firmware is giving you trouble.
The first thing to test is the JSON replies of the OpenSprinkler. To do this, type the following commands (do this when the UI is NOT working): /jn, /jp, /jo, /js, and /jc. The full URL would be: http://10.0.0.25/jn?pw=opendoor (for example).
Let me know if these work and we can further focus our efforts once we get those results.