Transporter Bug... Transporter Bug...
Only the host of a mission can beam around spare parts.
Obviously, in a solo mission, that isn't a problem, as the only player is the host...
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In a multiplayer though, that can get quite annoying (one time, someone was trying to send me a few spares, but I wasn't receiving them as I was the host and the bug was affecting his ability to send me a few spares...)