[Plugin: Fast and Secure Contact Form] Can not upgrade

Maybe your wordpress is requiring more memory than PHP has allowed it.

Try one of these methods for increasing the amount of memory a
PHP script may consume

1. If you have access to your PHP.ini file, change the line in PHP.ini
If your line shows 32M try 64M:
memory_limit = 64M ; Maximum amount of memory a script may consume (64MB)

2. If you don’t have access to PHP.ini try adding this to an .htaccess file:
php_value memory_limit 64M

3. Try adding this line to your wp-config.php file:
Increasing memory allocated to PHP
define('WP_MEMORY_LIMIT', '64M');

4. Talk to your host.

I’ve had exacly the same problem,
and your solution worked fine.
to be on the safe side I’ve used solution #3

worked like a charm. thank you.