Excel: MAcros and Locking

Hi,
I am using Excel 2002. I have few macros on my excel sheet. I have placed my excel sheet on web page. When user clicks to download, he get two options: Open and Save. If user selects Open option page displays but after that when he tries to use programmed menus (macros) and selects an option there comes the error. It says " ... file is locked for editing by 'another user'".

I am looking for help that how should i avoid this error.

Thanks in anticipation.