spontaneous compilation errors

[Mickey]

I am a classic asp and php developer so this compilation stuff is new to me.
What would cause pages to "spontaneously" develop compilation errors. They
are fine one minute and then poof, an error the next. The development
company's response is "It was an upload problem when we were making some
changes." But it happens several times every week, each time on a different
page. Is this a common problem with .net applications? What could be the
cause?

Thanks,
Mickey