PsTools : PsExec - Handle is invalid.

I am trying to use PsExec from PsTools to remotely install some software via a PHP script. Although I am having some issues when I execute the process via PHP (Apache). This is a sample error message below:

The handle is invalid.Connecting to <machinename>...Couldn't access <machinename>:
Connecting to <machinename>...

Although if I run the command via the command prompt on the same server, PsExec will run properly. 

The command I am using is: PsExec.exe \\<remotehost> -u "<username>" -p "<password>" -accepteula "<pathtofile>"

I have tried making the Apache service run under a local administrator account as opposed to the SYSTEM account but I saw no change. Although, I am able to run the ping command and hit remote hosts successfully. It seems that PsExec does not play well when other applications (other than command prompt) run it.

Any ideas?

Thanks,