@imagely – Thanks for your reply. Alas, I have just tried clearing the cache, reverting to a default WP Twenty Fifteen theme and only activating the NextGEN Gallery plugin – but the blank popup windows are still appearing for those four edit options.
I have also tried running on IE, Chrome and Firefox but to no avail.
Is there anything else I can try?
FYI, site details are:
Server Settings
Operating System : Linux (64 Bit)
Server : Apache
Memory usage : 23.75 MByte
MYSQL Version : 5.5.51-MariaDB
SQL Mode : Not set
PHP Version : 5.6.30
PHP Safe Mode : Off
PHP Allow URL fopen : On
PHP Memory Limit : 128
PHP Max Upload Size : 2047M
PHP Max Post Size : 2047M
PCRE Backtracking Limit : 1000000
PHP Max Script Execute Time : 86400s
PHP Exif support : Yes (V1.4 )
PHP IPTC support : Yes
PHP XML support : Yes
Graphic Library
GD Version : bundled (2.1.0 compatible)
FreeType Support : Yes
FreeType Linkage : with freetype
T1Lib Support : No
GIF Read Support : Yes
GIF Create Support : Yes
JPEG Support : Yes
PNG Support : Yes
WBMP Support : Yes
XPM Support : No
XBM Support : Yes
WebP Support : No
JIS-mapped Japanese Font Support : No
– Chris
