Most likely, you are running in to a permissions error.
I may be wrong here, but, this is what I suggest you check first.
The SQL Server service is started with a particular account. To see which account SQL Server uses...
Click Start -> Run
services.msc
Scroll through the list. You will see...
MSSQLSERVER
OR
MSSQLSERVER$instance name
Right click -> Properties
Click Log On tab.
The log on can be set the 'Local system account', or you can specify an account. In either case, make sure that the account used by the SQL Server service has access to the folder where your file is located.
* Note: This may not fix your problem, but this is where I would look first.
-George
Strong and bitter words indicate a weak cause. - Fortune cookie wisdom