I have found one temporary solution of it.
In app.manifest file, i have removed following line of code
<trustInfo xmlns="urn:schemas-microsoft-com:asm.v3">
<security>
<requestedPrivileges>
<requestedExecutionLevel level="requireAdministrator" uiAccess="false"/>
</requestedPrivileges>
</security>
</trustInfo>
now "OpenFileDialog" can access shared drive also.
Don't know why it is happning in Windows 10.
If above line is there then "OpenFileDialog" is unable to access shared drive.
If above live is removed then "OpenFileDialog" can access shared drive.