Ashurst was left red-faced after a misdirected email led to a dispute with its client over an underestimated fee arrangement.
The firm scrambled to patch up its relationship with software company Whereonearth earlier this month after an internal email between members of the firm was inadvertently forwarded to a member of the company.
It is understood that the email included a comment from one lawyer stating that he had never been confident of completing Whereonearth's sale to Yahoo! for the original quoted amount.
Ashurst said it was "inappropriate to comment on an individual client matter".
However, the firm's costs are understood to have spiralled because the transaction took six weeks longer and was more complicated than was first thought.
Colman Stephenson, fin-ancial controller for Whereonearth, said the company was pleased with the firm's assistance and that Ashurst had "absorbed some of the additional costs themselves".