Recently I suffered memory problems on one of my Wordpress single site installation.
I proceeded to disable all plugins and reactivate them one by one
Found out that the Paypal add on is causing an error when I try to upload media from the media uploader
Warning: Cannot modify header information - headers already sent by (output started at /home/ntdswp/public_html/dev/content/plugins/gravityformspaypal/paypal.php:5643) in /home/ntdswp/public_html/dev/wp-admin/async-upload.php on line 26 Fatal error: Out of memory (allocated 97517568) (tried to allocate 4800 bytes) in /home/ntdswp/public_html/dev/wp-includes/media.php on line 258
this is the error Wordpress gave me
If i disable that plugin (Gravity Forms paypal addon) everything went back to normal