If your company has enabled, Restrict GL Accounts by BU then you must make sure every business units have at least 1 active GL account associated with it. By not following this step, it will prevent users from submitting an invoice or expense report.
Below is the message that would be seen on each of the transaction module tabs.
1. Purchasing tab.
2. Invoices tab,
3. Expense Reports tab.
To see instructions for associating GL accounts to business units, see Managing GL/BU Association article.