I discovered that using a plus sign (“+”) in the password causes problems on some OpenSprinkler web pages. I can’t remember whether it was program editing or manual mode :|, but it wouldn’t work. I changed the “+” to a “.” and all was good.
The plus sign has special meaning in URLs, and since OpenSprinkler is controlled by a web interface, the problem is easy to understand. I’m not asking for the problem to be fixed, I’m just warning users not to use “+” in their passwords.