Endpoint Protection

   We have about 1500 clients that we need to upgrade from MR2 to MR4 MP2, and we're running into trouble. I've read some conflicting postings, some saying you can upgrade from 2 to 4 and others stating you cannot. When we launch the installation, it ends up installing the MR4 on the machine, but does not uninstall the MR2. If you then attempt to uninstall the MR2 from Add/Remove programs, you get a fatal error, but nothing helpful is written to the Event Viewer. I have tried upgrading the MR2 to MR3 first, but am receiving the same behavior on all clients. Has anyone else seen this, or can anyone offer some suggestions? My only option at this point is to uninstall completely, reboot, install the new version, reboot again, and be done - something I'm not looking forward to scripting for 1500 clients.

These are the supported migration platform for MU5 I would recommend you to upgrade to MU5 and check if you are still getting the same error.

Symantec Endpoint Protection 11.0.5002.333 (RU5) can migrate seamlessly over the following:

• Symantec Endpoint Protection 11.0.780.1109 (RTM), 11.0.1000.1375 (MR1), 11.0.1006 (MR1 MP1), 11.0.2000.1567 (MR2), 11.0.2010.25 (MR2 MP1), 11.0.2020.56 (MR2 MP2), 11.0.3001.2224 (MR3),11.0.4000.2295 (MR4), 11.0.4010.19 (MR4 MP1), 11.0.4014.26 (MR4 MP1a) and 11.0.4202.75 (MR4 MP2).
•  

 Currently you have MR2Mp1 installed ( 11.0.2010.xx ) so first you need to upgrade to MR4 then the patch for MR4 that is MP2.

So first upgrade to MR4 then to MR4MP2
or directly upgrade to MR5 which is already available.

I will try the upgrade to MR5. However, as mentioned, even when I try to upgrade from MR2Mp1 to Mr3 or MR4Mp1, I get the same behavior.

 MR2 is pretty old version which had too many issues with upgrade as well...so would suggest you to upgrade to MR5 by hook or crook.

I have attempted to run the upgrade to MR5 now, but am getting the same behavior. It is going to be horrendously difficult to uninstall the MR2 on 1500 workstations, reboot, then install the MR5 and reboot again. I can't believe I am the only customer experiencing this.

 When you deploy MR5 package what does it do ?
Do you have any packages assigned t othe groups if yes then remove them only add MR5 package and deploy MR5 package.

Migrating to Symantec Endpoint Protection 11.0 RU5 

Whether your SEPM is RU5
If you upgrade all your clients and SEPM only you can get all benifits of RU5..RU5 having a lot of fixes and new features...
ref:Release notes for Symantec Endpoint Protection 11.0.x and Symantec Network Access Control 11.0.x

The best method for upgrading your clients is assigning the packages to the Groups...
You can schedule it also...
If you are not upgrading SEPM now (Upgrade SEPM also is highly recommended) add RU5 package to SEPM console first, then only you will be able to assign to the groups> This you can do it in the admin---->Install packages tab... 

Latest Symantec version : 2010-01-13 rev. 026

Latest Manager version : 2009-12-31 rev. 126

Security response : 2010-01-14

Defination virus : 2009-12-31 rev.126

Symantec endpoint protection manager version 11.0.4202.75

windows server 2003 enterpise edition.

help me ???