Problem after attempting to install plugin - Fatal Error

I have got this error message after attempting to install the Pop-Up plugin through the WPMUDEV Dashboard:

Fatal error: Out of memory (allocated 71041024) (tried to allocate 297673 bytes) in /websites/123reg/LinuxPackage22/me/di/a_/media-care.co.uk/public_html/wp-includes/functions.php on line 251