This program cannot run because a reboot is in progress or software distribution is paused.

Really quick post here.  You may find when running an SCCM2007 task sequence from Run Advertised Programs that you get an error regarding another program is installing please try later. 

when examining the execmgr.log you will see This program cannot run because a reboot is in progress or software distribution is paused.

This worked for me - not claiming it to be a fix for everyone but you could try it.  On the problematic machine go to either:

• x86 – HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SMS\Mobile Client\Software Distribution\State\
• x64 – HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\SMS\Mobile Client\Software Distribution\State\

Set both "Paused" keys in there back to "0" if they are on "1" and then reboot.  Fixed it for me!!!