The constant _SVP_PAQUET_MAX_SIZE defines the maximum size of an archive fetched by the plug-in manager SVP. By default, this constant is setat 64 MB.
You can customize this value in your file config/mes_options.php (see the article dedicated to it).
Example :
// allow retrieval of over 64 MB of plug-ins
define('_SVP_PAQUET_MAX_SIZE', 128*1048576);