[Plugin: VoucherPress] Memory allocation error

I got this error when I tried to update the VoucherPress plugin.

Fatal error: Out of memory (allocated 53477376) (tried to allocate 15051631 bytes) in /home/mysite/public_html/wp-includes/class-http.php on line 1408

This is line 1408:

1407 if ( strlen($theResponse) > $headerLength )
1408 $theBody = substr( $theResponse, $headerLength );
1409 else
1410 $theBody = ”;

I followed the advice in another post and doubled my php memory allocation via GD Press Tools. Still get the error, although I am able to update my other plugins with no problem.

Any clue as to what’s wrong?