As terra incognita points out - this is a security issue.

For ASP pages, if you allow anonymous access, the pages run with a local computer account named "IUSER_<machine-name>". This account typically cannot access shares on other computers.

The simplest solution for you may be to TURN OFF anonymous access to the page, and make sure whoever accesses your page has access to the remote share.

More complicated solutions involve creating an appropriate domain account, and making the page a part of a web application that runs under that account.