It looks like your PHP memory limit is set too low, and the script needs more.
Although the script uses little RAM to display the grids, it needs to allocate enough RAM to be able to pre-process the Grids in the Admin.
The default memory limit setting should work well if you have your grids at 100 rows by 100 columns (million pixels), however you will need more RAM for bigger grids.
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Instructions if you have version 1.6.3 or later
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Please try to increase the memory limit setting in the Main Config.
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Instructions if you have version 1.6.2 or earlier
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Increasing to 12MB usually helps.
If you are running apache, you can try this:
Create a .htaccess file in your web directory (or modify if the file is
there) and add the following line to the file:
php_value memory_limit 16M
If your hosting accound does not support .htaccess, add the following
line to include/functions.php file below the first <?php
ini_set('memory_limit', '12M');
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If that does not work, then how big is your grid??
The script can get very thirsty if there are more than 10,000 blocks
per grid (1 million pixels) so check if you didn't set it to something
really big! Or…you may have a really big background image that's
causing the trouble.
Please note that this is not memory as in storage space on disk, but memory as in RAM. Most hosting companies provide 8MB by default, and that is enough for 1 million pixels.