Cofunds is continuing maintenance on its capital gains tax (CGT) calculator following fresh complaints from advisers.
The Praemium-powered tool, launched in November 2007, has been unavailable to advisers since the beginning of the year due to an undisclosed "bug". It is expected to be fixed by 10 January.
The platform first withdrew the tool in October, after advisers pointed out it valued the gross rather than base cost of the fund.
It meant clients may have undervalued the cost of their investments and paid too much tax.
However, a spokesperson for Cofunds said the current problem was a separate issue to gross valuations.
"It's not the same problem as in October," she said. "There is a bug in it which we are trying to fix. It's maintenance to ensure it is up and running fully effectively: we don't want to have it up there if it wasn't running at full power."
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