cannot hit website .aspx file

We have an app / website that i cannot reach on one particular server. When i try to reach, i get the following error message
"Server Error in '/' Application.

Runtime Error"
In IIS logs, it generates this line of error:
2015-03-13 11:12:08 GET /index.aspx - 80 - Mozilla/5.0+(Windows+NT+6.3;+WOW64)+AppleWebKit/537.36+(KHTML,+like+Gecko)+Chrome/40.0.2214.115+Safari/537.36 - 500 0 0 124270

The site works on another server. I have compared all the IIS settings and used exactly the same files.
Also. If i create a .txt file and put it in the folder, then i can hit that no problems, so i'm thinking it must be an aspx issue of some sort.

Does anyone know what the 500 0 0 124270 error means in the IIS logs. Ive already looked up 500 errors and worked through the, I'm more interested in the numbers after and if they can help me find the issue.
Or any other place i should be looking.

Thank you
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David Johnson, CD, MVPOwnerCommented:
is the applicable .net framework installed on that server?
Manoj PatilSr. Software EngineerCommented:
Is your Server Folder is same as your Project structure
There are several reasons for this kind of issues.

Can you post the error screenshot. So that it will be easy to understand it ?

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jamiegfAuthor Commented:

Both environments have exactly the same .net frameworks installed (fully up to date).

The folder structure is also the same in both environments.

Here is the web page error below. (The IIS log errors are in the main description)
David Johnson, CD, MVPOwnerCommented:
That error message isn't helpful except that it tells you exactly how to display the error so it can be diagnosed. by modifying your web.config as it clearly shows you
jamiegfAuthor Commented:
This was pretty much it. The folder structure was the same, however, permissions on a certain folder were different. IIS user needed modify permissions.

Thank you!
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