Trading on the Nordic OMX bourses began five and a half hours late on Tuesday.
The exceptionally long blackout, which followed a similar 40-minute delay experienced on Monday, was apparently caused by a software glitch that locked out clients and meant that trading in Stockholm, Copenhagen, and Helsinki started only at 15:30 local time in Helsinki.
Baltic and Icelandic bourses were also hit.
A new system upgrade was blamed for the halt, which is hardly likely to inspire confidence among traders.
It is thought to have now been resolved, and problems are not anticipated on Wednesday.
