I am on 2.50+ Build 160504 and want to randomly ask one question per group. I downloaded the survey template "limesurvey_survey_55164.lss". It used to work on earlier versions of LimeSurvey, but not on my current installation.

Here's what I did:

1. Downloaded the survey template limesurvey_survey_55164.lss from www.limesurvey.org/manual/Expression_Man..._Surveys#Download_10
2. Imported it to my installation of LimeSurvey
3. Clicked on "test survey"
4. Read the welcome page of the survey
5. Clicked on "next"
6. Wondered why nothing happened

I tried activating the survey. In the activated survey, I get the error message "Did not save An unexpected error has occured and your responses cannot be saved." when I click on "next" a second time while viewing the welcome page.

Is this a bug?

The sample survey was created for the older version of LS. The new LS 2.5 has been changed significantly and this is probably the reason for the error. Maybe try to create a new survey in your LS and implement the instructions provided in the manual in your questions. I mean the relevance equations that are shown in the example.
Regards

Edit: I checked the example survey in my latest version of LS (2.50+ Build 160517) and it works.

You're correct. I tried the example survey with another installation of the latest build of 2.50+ and it worked perfectly. There seems to be something wrong with my other installation and I can't seem to find out what.