In the hours before the deadline on Monday evening many people had difficulty logging in using their electronic bank identifications and primarily affected customers of Swedbank, Danske Bank and Handelsbanken.
"Just as on Sunday night it has been difficult for many people to log in using their bank identification. It is a question of capacity, the servers for the bank-ID do not have the capacity when a large number of people try to use it simultaneously," said Erik Boman at the agency.
Boman suggested that all those unable to log in should follow the instructions in the error message and try again later.
The agency has now extended the deadline until the end of Tuesday to enable any that are still unable to log in and file their taxes online can hand them in manually.
"If you tried to submit your declaration this evening (Monday) and have not succeeded then no late filing charge will be levied if it is handed in tomorrow. We are also able to see if you have made an attempt," Erik Boman said.