Click the following link to download the Symantec Endpoint Protection (SEP) 11.0 RU6a Client-only patch (64Bit) for SEP 11.0 MR4 MP1a:
ftp://ftp.symantec.com//public/english_us_canada/products/symantec_endpoint_protection/11.0/updates/SEP64_26To562_clientMSPMSI.exe

Release Date: April 26, 2010
Description: This patch upgrades Symantec Endpoint Protection 11.0 MR4 MP1a 64-bit Clients to version 11.0 RU6a.

NOTE: This patch will only upgrade 32-bit Clients. If you need to upgrade your Symantec Endpoint Protection Manager to 11.0 RU6a you must download the complete update from File Connect.
once you have upgraded the manager to 11.0 RU6a you can also upgrade clients using the auto-upgrade mechanism built into the Manger console.

For additional information about changes in Release Update 6a read the Release Notes. An MD5 file is also available.