This article is from the Star Trek Tech FAQ, by Joshua Bell inexorabletash@hotmail.com with numerous contributions by others.
One would imagine that shield and transporter technologies are in a
constant development race, as sensors and cloaks are. The "enemy" is
always trying to figure out a way to transport through your shields,
and thus you must always be trying to improve your shields to block
this. Hence, any 70-year-old shields, like those on the Jenolan, would
be practically transparent to modern transporters.
Alternately, Geordi and Scotty knew that the Enterprise would have to
beam them off the ship, and turned off the "transport blocking"
frequencies in the shields.
 
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