The message "Update already in progress" is issued under two sets of circumstances.
You are updating one of your records in one browser window and you start another window and try and update the same record. The message is issued in order to warn you may be about to overwrite any changes you have started in the first window.
In this instance close the new window and complete the update in your original window.
You started to update a record or add a new record but you did not complete the update and did not use the "cancel" button. You will receive the message the next time you try to update the record.
In this instance you have the option to either resume your update where you left it or discard the changes you had previously started.