Hi,
You mean the menu named Invoicing is Missing ? If so check whether there is a menu named accounting there. If accounting is there, the invoicing menu get renamed to Accounting when the accounting module is installed.
If accounting menu is also not visible, switch to the Super user mode and see whether the menu is getting visible now, for switching into super user mode, see this: Super User Mode
If the menu get visible now in the super user mode, the reason for menu not visible earlier is due to access rights issue.
Even in the super user mode if the menu is not visible, activate the developer mode and navigate to Settings -> Technical -> User Interface -> Menu Items and search the menu here.
Still if it doesn't work, upgrade the module once again and see.
Thanks