This error is caused by the user not having enough permissions in Dimensions.
To resolve this issue:
Log into Dimensions.
Click System, Profiles.
Scroll through the profiles and select the profile that the affected user is in.
Click Edit.
Next to Sales Orders, click the red cross to change it to a green tick. If it is already a green tick, continue to the next step.
Click the words Sales Orders to expand the section.
To disable all sections other than Transactions, click the green tick to turn it to a red cross. You may also be able to disable some options within Transactions, but you will need to do this on a trial and error basis as some options will be required depending on your Sales Request setup.
Click Save.