ProFTPd connection closed

[CJZ]

Recently, around April 20th/21st, my server has been dropping FTP connection, noticable on larger files. The following is details:

--Server--
Centos 5.8
Plesk Panel 11.09 Update 48
psa-proftpd 1.3.4c-4.el5.art
-----------

--/etc/proftpd.conf (items added after)--
TimeoutSession 0
AllowStoreRestart on
-----------------------

--FileZilla Response --
Error: Could not write to transfer socket: ECONNABORTED - Connection aborted
Error: Connection closed by server
Error: File transfer failed after transferring 32,505,856 bytes in 59 seconds

Error: Could not write to transfer socket: ECONNABORTED - Connection aborted
Error: Connection closed by server
Error: File transfer failed after transferring 32,440,320 bytes in 59 seconds

Error: Could not write to transfer socket: ECONNABORTED - Connection aborted
Error: Connection closed by server
Error: File transfer failed after transferring 31,981,568 bytes in 59 seconds
-----------------------

-- /var/log/secure --
www proftpd: pam_unix (proftpd:session) : session closed for user ****
----------------------

On large files (testing with >1GB), it lasts about 1 minute before the connection closes. The 'AllowStoreRestart' was added to work around this error. ProFTPd was updated to the latest after this occured (and still occurs). Any suggestions would be appreciated as I have no clue what is causing this. It worked for months before April 20th.