LimeSurvey version:
5.6.3
Own Server
Theme/template: Fruity default
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When a user completed a survey they ran into this error message. 
Another user experienced this issue when starting the survey. 
Any ideas what is causing this?

 

You need to activate www.limesurvey.org/manual/Debug_mode
Then we have more information

Hi There,
I turned on debug and have attached the output of the error in a TXT file and a PDF, whichever is easiar for you to parse.

Please let me know what you think.
Thanks!

The error shown don't seems to be the same … are you sure you do same action ?
Here : it's the error shown when previewing survey.

Else : you have some plugins ?

I also have this problem, is there any way to avoid or fix this problem, please reply

A quick test would be to try to open the link in incognito mode or similar. Chrome gave me this message. I tried in incog mode and it worked. Afterwords it is working without the need for incog window. Weird.

FF works fine.

May be adblock or similar pluginn?

HTH

Here you are the latest update of this problem.

I extend the bootstrap theme and add my own custom.css file, and once I did that I got an error above.

LS v6.4 under Linux.  Please find the screenshot for the problem.

By the way, here are what I did:
- I upgrade LS from 2.x to 6.x
- Then extend a theme from Bootstrap
- Then in Survey general setting, I update the theme from "Inherit" to my custom theme
- Click the link shown on "Shared survey"
- Error display

If you roll back the selection to inherit theme, then click "Run the survey" again, it works fine.