This is caused by Transaction Broker looking for a log file in a location it either cannot find, or that the log file doesn't exist in anymore.
To resolve this, follow the below steps:
Create a text file used for logging. This is best placed in the Transaction Broker install folder, typically C:\Program Files (x86)\Access Applications\TB\2.51f. To create a file, Right Click in blank space in the folder and go to New > Text Document
The file can be named anything, but EventLog will help identify the log when checking for errors in future.
Now we need to point Transaction Broker at this file. To do so, within Transaction Broker click on Transaction Broker
Now click System Options...
In the Event Log tab, click on the Folder Icon to select a location
A new window will appear which should be the Transaction Broker install location, from here navigate to where you created the log file, and Double Click the log file to select it
Click Save at the top left to save the changes