In OJS 3.2.1.2, While assigning an article to an issue, an error occurred " An unexpected error occurred. You may have been logged out. Please reload the page and try again".
The screenshot is attached. 
@asmecher kindly assist us to resolve this issue.
Have you reloaded the page and tried again?
Yes, but still not working.
Similar thing happens to me: OJS 3.2.1.2 Error with publication - cannot publish issue
But nobody helped…
Looking at your screenshot, I see that your server is returning a 405 status code. This means that your server does not accept the HTTP method. My guess is that your server is not configured to support PUT requests.
We’ve addressed this issue but the fix will only go out with v3.3, scheduled for release in early February. In the meantime, I suggest that you try to adjust your server configuration to support PUT and DELETE requests.