This error occurred when trying to adjust a Pledge Transaction.
A Pledge Transaction (or probably any Transaction) cannot be adjusted if the Bank Approval Status is 'PE'. The E-GM126 error is the result of trying (when doing an error check of the Batch Detail item).
There are reasons a Transaction could be left in this state. If, for instance, an EFT or Charge Processing job failed due to a connection issue, the Transaction could be left with Bank Approval Status = 'PE'. TA puts the Transaction in that state until SAGE responds and confirms that the charge was processed. If a connection problem occurred, the Transaction would never be updated properly. Research would need to be done to determine the job that caused the issue (i.e. if there were more Transactions left in this state), and then steps need to be taken to reset and correct the Transactions.