Endpoint Protection

 The date will be 31.12.2009 but revision number will change. 

https://www-secure.symantec.com/connect/forums/official-status-sepm-definitions-stay-31-12-2009-last-updated-07-jan-2010

 Today, Revision number is 119.

But it's not the answer of the issue; my problem was all about the .jdb file, not the definition date..

Whether your SEPM installed in c drive only?
 What is the current date of definitions present in your server?(You can find this in Admin---->Severs---->local site---->show liveupdate downloads)
After pasting the file after processing it will get disappeared from the location were you are pasting.Whether it is happening?
If you paste the jdb file it will take some to get it installed
If you came to admin tab downside it will give that message.
What was the extension while you are pasting the file in server?
It should be .jdb some browsers while downloading this file will change extension to .zip. If it happens you have to again change back to .jbd before pasting.
Also download a new jdb file from here and try to paste it.The location you are refering ({C60DC234-65F9-4674-94AE-62158EFCA433}) is the updates for 32 bit. Assure that while downloading jdb file you are downloading 32 bit version.

download the jdb and paste it again.
to the incoming folder
restart symantec endpoint manager service and check 

Yes, it's only installed in C drive and current date of definitions is 31-12-2009 rev.118 which I manually installed yesterday.
After pasting the .jdb file, its name changed as "VD2F3E76.jdb.2010-01-07-14-25-42"  folder but did not get disappeared. I have waited for a couple of hours but nothing has occured.
Firstly I'd changed the extension from .zip to .jdb, but I re-downloaded just the .jdb file and copy to the specified folder. Still cannot see this update in ({C60DC234-65F9-4674-94AE-62158EFCA433}) folder either..

Ok then I will try this..

check if you have followed the same steps as mentioned here

http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007100820002048

Your SEPM is up to date
check this thread
OFFICIAL STATUS: SEPM Definitions stay at 31-12-2009 (LAST UPDATED: 08-JAN-2010) 

I copied the .jdb file which I downloaded today and its name is VD2F3E77.jdb to the specified folder, after a couple of seconds the file and temporary folder disappeared, but both SEPM and the client definitions remained the same..

I'm sorry, i forgot that, JDB should work without any issues
when it processess you should see two numbered folders
one for 32 bit and 64 bit
do you see just one numbered folder? 

 SEPM will show 31-13 but it is current definitions.Once the other issue is fixed SEPM will strt showing the correct date.
If the Clients are getting updates from SEPM it will show wrong date.
However if you run intelligent updater manually on the client it will show the right date.

So even though your SEPM sows 31-12 definition date but you have current definition and you are protected.

Just one numbered folder for 32 bit had appeared and then disappeared. I thought it began to work and install the definition to SEPM and the connected clients but after 2 hours nothing has changed..

 No matter what you try SEPM does not  ( yet ) have the ability to show 2010 definitions.
So it will remain at 31-12 till a fix is released.
New JDB contains current definition till date however in SEPM it will only show 31-12 definition.

Vikram is right you have to wait till that patch is getting released.Refer the link which I had pasted in my earlier post.You will get latest information about this issue.
Now you can confirm your SEPM is up to date with the help of revision no. 

Okay then, the definition is updated on SEPM, its allright.
But the issue I "really" wonder is not the definition DATE, the issue is how it will occur on the other SEP clients by the means of this .jdb file in the SEPM server. I can see the newly definition date just on my management server, not on the clients... 
Tried to explain it clearer.

 If your Definition on Clients is 31st December 2009 rev 121.
Then you have current definitions ( which includes signatures till 10th Jan. )
https://www-secure.symantec.com/connect/forums/official-status-sepm-definitions-stay-31-12-2009-last-updated-10-jan-2010

 

Patch for RU5 SEPM is posted on LiveUpdate Servers

Symantec Endpoint Protection Engineering has confirmed that the patch that enables MR5 SEPM to download content dated 2010 has successfully posted to our LiveUpdate servers.  Please note: it will take a total of three LiveUpdate cycles to prepare the SEPM, download the patch, and begin using and distributing 2010 definitions.   If you have manually configured their SEPM not to download the patch via LU can apply the patch manually using a standalone tool.  For more information about the issue and the patch, please see the following KB document: 
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2010010308571348