Outlook 2007 Send/Receive stuck at 50%

Are you using Outlook cache mode? try switch to online mode and see if the problem remain
You can also test it from OWA

Did you try load Outlook in safe mode?

Start->Run->Outlook /safe

maybe there is add-on that cause this

Possible Outlook OST corruption if its huge.
Any Av or Addons ?
Have you updates Outlook with the lastest SP and patches ?
Is the OS different for these user ?

Did you try creating a new Outlook profile ?

- Rancy

Ya I got your problem I ill suggest you  please ping your server first if its getting continuous reply without RTO and just go the control panel then add or remove programe and repair your office, it ill solve out..m sure ill solve out problem,..If not then back to me.

The problem appears to be on the receiving side of the connection; Outlook sends first, accounting for 50% of the activity, and then stalls at receiving. This is further confirmed by the fact that new emails don't appear until Outlook is restarted.

If Outlook is configured to run in cache mode, the user's .ost file may be corrupt. Close Outlook and delete the user's .ost file. Then open Outlook; this will cause a new .ost file to be built - if the user's mailbox is large, this may take some time. Then see if send/receive works as it should.

I tried switching from cached mode to online, but the problem remains.
I noticed that when this happens, if I CTRL+Right click on Connection status on the Outlook tray icon, under Local Mailbox it says Offline address book Connecting to Microsoft Exchange.
If i try to separately download just the OAB from Outlook it gets stuck on Processing indefinitely and produces no error code.
I can ping and get a reply from the Exchange server when this happens.

Have you tried to re-create the Outlook local profile?
This is happening for all users?

Yes, I tried re-creating the profile, it didn't help.
The OAB issue seems to be affecting all users.