The ban was imposed after the League One club took out a short-term loan with the Professional Footballers' Association.
But a statement on the club's official website confirmed the money had been paid back in full.
Blackwell could only name four substitutes for Saturday's draw at MK Dons but will now be able to deal in the January transfer market.
The statement, posted on Friday afternoon, read: "The club can confirm that the loan taken from the PFA has been repaid in full, and as a result of this repayment, the transfer embargo applied to the club by the Football League has been lifted.
"The club are now free to sign players as required."