Script commands are linear.. one doesn't start until the prior completes. Still sounds like a network-ready issue.
The drive disconnect process doesn't require a valid network connection, but connections do. Thus, the script can complete the disconnects quickly before starting the connections.
I'd add a Sleep 5 as a temporary measure for testing.. if the problem goes away, it's timing. You might want to ping the host before trying the first connection, waiting for a response. The Ping() UDF that I wrote can be used to send 20 pings with 1 second intervals, but will return after the first response. This would be a simple way to perform a connectivity test while minimizing the delay.
You should still get to the bottom of the issue, as the above suggestions are work-arounds for the real problem. Look into the GPO setting that prevents network connections before the workstation network is ready. (wait for network)
Glenn
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am a Rocket Scientist!