Filofax paid pounds 5.4m for Henry Ling & Sons four years ago but has sold it to a private buyer for a maximum cash consideration of pounds 1m.
The deal includes a goodwill write-off of pounds 4.8m.
The news, combined with a trading update warning that the strength of sterling was still affecting trading in the second half, knocked 9.5p off Filofax shares which closed at 187.5p.
The company repeated the announcement it made in February that it was continuing discussions with third parties in relation to various strategic opportunities.
It is thought these could include a bid for the whole group, which at yesterday's share price was valued at pounds 53m.
Filofax said that in spite of the currency impact, sales had grown in all areas apart from Henry Ling, which it said was experiencing a disappointing year.
The company said it expected profits for the year to March to exceed pounds 6m. Previous forecasts were for pounds 6.5m.
These forecasts included an expected contribution from Henry Ling & Sons, which made profits of pounds 188,000 last year and had net assets of pounds 2.4m.
Filofax has been struggling over the last couple of years due to the increasing popularity of electronic organisers and, more recently, the strength of the pound.
The company's shares reached a peak of 275.5p in 1995 but slumped to 121.5p last November after a profits warning.