The council is suing ICL to get its money back. Others who lost money are watching with interest, St Alban's counsel Richard Mawrey QC said.
In 1989, the environment secretary sent all councils a form on which they had to enter the number of poll tax payers they had.
In St Albans, ICL's COMCIS revenues program printed out a figure of 97,000, which was entered on the form and returned to the DoE.
In defence, ICL claimed St Albans failed to take adequate steps to save itself from the computer software error.
The company admits there was an error in the software, but claims St Albans was partly to blame for the loss. The council's own estimate of the true number of adult poll tax payers in its area at the time was also hotly disputed.
'Our case is that St Albans DC could and should have realised that the only way they would get an accurate result was to use all means available,' said Timothy Lamb for ICL.
He claimed the council was well aware there were bugs in the software installed by ICL to cope with the change-over from rates to poll tax.
But it had failed to double-check the figures put out by the computer by analysing the 'hard copy' results of its canvassing of all homes in the area.
The court heard ICL had kept no copies of the now obsolete software package and the exact nature of the error will probably never be known.
The case is expected to finish today.