Mac excel 'read only' problem?

[sunnyhanda]

I have this network setup for one of the company that owner handles and recently we start to have problem with mac ms excel file. this xls file is being shared on network drive and accessible to only 2 employees (accouts) but what happen is even though none of the person has opened the file and when any of them tries to open it up it opens but with read only thing and for that reason i had to go there and restart the both system and then it works fine. i have checked all the permission level and its read n write for both them. what should i do? its getting into our nerves...
thanks