When suspending/resuming a system with RHEL5, Network manager often does not see anymore Networks Interfaces after resume. This has been reproduced with ipw2100, 2200 and 3945 based wireless cards in Thinkpad laptops with 5.0 and 5.1 Beta. It failed in 6 of 10 cases (tested approx. 40 cases). While it at this point is unclear whether the problem is in NetworkManager or in the wireless drivers, the fact that it also does not see the ethernet interface suggests that it is NetworkManager. Restarting NetworkManager IS a workaround that helped in every case during the test. At least in the caes tested for this, also deactivating networking in the NetworkManager menue and then re-activating it helped. So a short term solution might be to add a NetworkManager restart to the gnome-powermanagement quirks.
So, notting just ran into this issue as well and adding "sleep 2" just before the dbus-send call fixes this. Looks like a race...
This should be fixed in 5.2 by a combination of #215720 and #362421. Can you test with the version of NM in 5.2 Beta (0.6.4-7.el5) ?
This was fixed in 5.2 and fix will also be present in NM rebase in 5.3.