CSV Import: constant error, unable to even try again

I have a problem with CSV import. Initially it let me access the initial form (where you specify the location of file, delimiters etc), after Next it reports constantly

Bad Gateway!

The proxy server received an invalid response from an upstream server.

The proxy server could not handle the request GET /ukauka/arhiiv/admin/csv-import.

Reason: Error reading from remote server

If you think this is a server error, please contact the webmaster.

Error 502


Webmaster says - server reports, it takes too much time (my file is small, for just a try, 76 kb).

But the problem is - I cannot even try again! If I press the csv export button on the administrators navigation bar - then the error report appears. I have tried to uninstall and reinstall the plugin, but this did not change anything.

Any ideas?

Thanks in advance

It turned out the problem was in the limits of memory usage of PHP scripts in the server. FWIW