This error can happen in many parts of the business logic due to the fact that it is about permissions to access, read, and execute certain parts of the database, and more to the point the inability to do this above.
If a database job is being run on a scheduled automatic basis, as part of configuring the job our DBAs must input which user is the virtual runner/executor of this job. If it is JBLOGGS then this error might appear at runtime as it is likely JBLOGGS user doesn't have enough high level permissions and privileges to be writing interacting with the database with regards to some of its objects.
The FW user on the other hand is likely to have these permissions and privileges as it is typically a high level/system admin level user. And so, when the code that the job is running says look in this part of the database and write to it, this error will not appear as this user will have been accessing successfully.
In this case it's not about the user name per se, it's really about the permissions and privileges the user name has assigned to it that is the key. It could well be that JBLOGGS would be assigned the permissions needed and FW not so, unlikely but in theory possible.
So, the resolution here would be to raise a new case online and reference the title of this article.
We will then speak internally to our DBAs to look at the error, what user is running the code, and to check that this user has the permissions granted to it that it needs to access and do what it needs to in the database.