When running the version of Pear that comes with MAP you may get the following:

Notice: unserialize(): Error at offset 267 of 1133 bytes in Config.php on line 1050
ERROR: The default config file is not a valid config file or is corrupted.


The solution is to delete the conf file, located here (path may vary slightly):
/Applications/MAMP/bin/php/php5.3.6/conf/pear.conf

That’s it.