Maximum File Size

i have an excel file size 18mb which i was working on this after noon, i now come home this arvo and open it and its telling me the excel file can not be opened

It gives me the error
[filename] cannot be accessed. The file may be read only or you may be trying to acess a read-only location. Or, the server the document is stored on may not be responding.

all my other excel spreadsheets work on the desktop and i placed it directly on c drive and it game me the same msg...

any ideas???