you can delet them
you need to withdraw the policy for all the groups before y ou delete them.
opem sepm
click on polices
select type of policy
on the right, just highlight the policy ,here you will see location use count, saying howmany groups have that policy assinged,
once higlighted
on to your right you will get withdraw policy at the bottom
just select that and withdraw

P.S: you need to assign new policy before you withdraw old one, coz it willbe in use

Is there a tab / section in SEPM that shows all the policies?

you need to click on policies tab..
there you will find all the policies, and the location use count for each group.

Would it be better to withdraw the policy or replace it? What's the difference to SEPM? Is there a document out there on this?

Thanks for all your help

Yes the policy can be deleted.

But make sure that the policy is not assigned to any group. The location use count should be 0

 You can withdraw or Replace policy however you cannot delete the default policies.
So you can create a new Policy and while assigning it make sure you assign it to all the groups.
You can confirm that by Location Use count on the policy.

SEPM - Policies --when you highligh a Feature on the right it will show all the policies and the location count.

It is better to withdraw the policy rather then replacing or deleting it.

When we withdraw the policy , the policy is not assigned to any group but it is still in SEPM so if required it can be used later

Title: 'How to remove inherited Policies in the Symantec Endpoint Protection Manager (SEPM)'
Document ID: 2009032012404748
> Web URL: http://service1.symantec.com/support/ent-security.nsf/docid/2009032012404748?Open&seg=ent

Thanks all

I think I will be replacing the policy

I'm confused as to why I see clients with different policies, communication between client and SEPM is good.

Is there a default location on C drive where policies are stored?

Also, I should have mentioned that I only have one policy assigned to all locations. Changes (different policy dates) are made from time to time and its the changes that the clients are not getting. So if I add a rule to block USB, some client get it and other don't meaning some USBs are blocked and other are not.

export your current policy, just rename it to something else
import it again, and assign this policy to your groups. its same policy but forcing clients to get it
check if they are able to download it now. 

Is it possible for the policy to become corrupt on the client? And if so, can it be deleted manually?

I am not sure about this .But it may happen in case of a infection. If there is a threat that attcaks SEP , then it is possible.

Policy on the clients is stored in files , the files can be deletd or replaced, but i have not tested that . But first try to test this in the test environment rather then going with it in production

Title: 'What settings are stored in each of the .DAT files in the Symantec Endpoint Protection 11.x folder?'
Document ID: 2007090610224048
> Web URL: http://service1.symantec.com/support/ent-security.nsf/docid/2007090610224048?Open&seg=ent

on one client machine i would like you to delete the backup file, these are the once which takes place if smc is not able to read the latest one
delete the .bak files
Server.dat.bak
Serdef.dat .bak
apply ur new policy

I have done this, I will update shortly on what happened

Didn't appear to work. I tried "Update Policy" as well. It either doesn't grab it or reverts to an old date. I already called Symantec and suggested everything I tried on the forums so not sure what else to do.

How do you confirmed communication is ok between client and server?
Whether all the clients having the problem?