The maximum recommended length for a parallel cable is 20 feet. Mixed
results will occur for distances greater than this depending on the
type of cable (shielded vs. ribbon) used and the quality of the
connectors. There are other solutions available.
In the United States there is a company called Black Box that sells a
product called PC Parallel Hypercable which allows parallel cables to
be extended up to a maximum length of 150 feet. Each cable
incorporates an integrated amplifier circuit that boosts signal
strength and filters noise. The circuit is powered off of the 5 volt
signal that is available on pins 13, 14, 15, or 16 of standard
parallel interfaces.
For more information look in the Technical Information Library, using
"Black Box" as your search string. Similar information may be
available from European companies.