Error is: document has been modified after you have opened it

hi,
getting this error: document has been modified after you have opened it. its appears when customize form and edit sales invoice

Normally happens when you have multiple windows open of the same doc , the one instance of the doc is edited , so when you revert back to the other instance of the doc the system will notify you that the document has been modified and you would need to refresh…

thank you, sorry for the delayed reply