This could be that the transaction you are trying to authorise exceeds your authorisation limit. To check and amend this:-
Go to System Admin
Then User Set up,
Click on the relevant User Name from the list
Then click on Company
Then Properties
Go to the Limits tab and check the amounts
To amend the Limits right click Modify Record
Enter the new limit
Apply to Save
If the above does not resolve the issue for you. Please raise contact us, reference the title of this article, and provide details of the User Name and the transaction, screenshots will be useful, showing the User Limits and transaction details.