Are your post/request URLs online? If so, it is probably a cross-domain issue.
[quote:2mg5dmmw]Making AJAX requests cross-domain or in preview
By default, browsers block AJAX requests across domains. This means, for example, a game on scirra.com can request other pages on scirra.com, but cannot request pages on facebook.com. This is an important security feature of web browsers (it is not specific to Construct 2 or its AJAX object).
Also, when previewing in Construct 2 the game runs on localhost. This counts as a different domain to the rest of the internet, so typically AJAX requests to any web page will fail during preview, unless the server explicitly allows cross-domain requests.
If you want AJAX requests to your server to work from any domain, or in preview, you can configure it to send the following HTTP header:
This will enable AJAX requests from any domain, but you should still be aware of the possible security implications of this. For more information on cross-domain requests see HTTP access control on MDN.
If it is a local post/request, check your file pathing.
[quote:2mg5dmmw]Using file paths correctly
Never hard-code paths (such as using an action to write to a fixed file path like "C:\MyGame\MyFile.txt"). This unfriendly to users, and is often perceived as unprofessional, untidy, or filling the user's system with junk. Not only that but in many cases it simply will not work, since not all users have permission to read or write to folders outside of their user directory.
It is tempting to solve this by writing files to the application's folder. However this also may not work; on many versions of Windows, the Program Files folder requires administrator permission to write to, although you can read from it.
The solution is to write to the user's folder, which you almost certainly have write permission for. This is provided by the UserFolder expression. The correct way to determine a file path in the user's folder is like this:
NWjs.UserFolder & "myfile.txt"
If you only need to read files, and don't need to write them, you can safely use the application folder (NWjs.AppFolder) instead.