The version of LimeSurvey is: 3.28.57, we own the server it is running on and the theme that we mainly use is EQ-5D-LStheme 

To attempt to resolve the issue, we have tried, restarting the server and installing the latest version of LimeSurvey and the user is the owner of the survey. 

The issue we have is, on only some surveys, when a user goes to the data entry page, it tries to load the page and but we get the following error: "This page isn't working. website is currently unable to handle this request. HTTP ERROR 500. The error is very generic.... and the logs so far have not been helpful. 

This only happens on some surveys, not all of them. 

Has anyone else seen these issues before/ and if so, what is it that you did to fix it? 

Your installation of LS is fairly up to date, but before I would start any bug research, I would update to the latest version.

Since when does the issue appear? Was it OK before?

Also, when errors happen, always try with a standard Limesurvey theme before anything else. Often the problem is the custom theme.

HTTP ERROR 500 is a server error, so these often have nothing to do with Limesurvey, but rather with a server configuration.

As this happens only with some surveys, try to make a copy of a survey with the problem and see what happens in this copy.

Try activate debug mode to understand the issue

manual.limesurvey.org/Debug_mode

Maybe memory issue

Thanks for the reply, sadly it doesn't seem to be the theme that is causing the issue this time

What do you mean by "data entry page"? For me that is the page when you edit or add responses in the backend of LimeSurvey. If that is the case the survey theme cannot be relevant.

But you seem have a different understanding.
Data entry page is just when an activate survey is visited as an respondent to start the survey, right?

What webserver is used? What version of PHP is used?

DenisChenu wrote:

Try activate debug mode to understand the issue

manual.limesurvey.org/Debug_mode

Maybe memory issue

jelo wrote:

What do you mean by "data entry page"? For me that is the page when you edit or add responses in the backend of LimeSurvey. If that is the case the survey theme cannot be relevant.
 

I assumed that he is talking about "Responses" --> "Data entry screen":
 

I wasn't aware that this doesn't have theme screen, but it makes sense, this is in the backend and thus has nothing to do with the survey theme. So my hint about the theme was probably not very clever.
 

Yes, this is correct, it's that page.

I did a Chrome Network trace on it, and when I click the button on the data entry screen option, chrome didn't actually trace that the button had been clicked.

So it's almost as if something is being blocked straight away... the weird thing is it works on other surveys.

Did you test with a copy of this survey as I suggested? Just to see what happens?

Just an update, when I click on it, the error reported by Google seems to be: (failed)net::ERR_HTTP_RESPONSE_CODE_FAILURE for this link: /index.php/admin/dataentry/sa/view/surveyid/*surveyid*

I did a copy of the Survey and the error still happens. 

So it would suggest it is a Databse issue?

I would create a bug report for it.