In Windows Mobile, when you activate a network card, you need to set it in either "Internet" or "Work" mode. In order to access local network resource such as shared folders, your network card must be in "Work" mode.
In order to change the current mode, go to [ Start ] -> [ Settings ] -> [ Connections ] -> [ Network Cards ] (for some devices, the option is found under [ Start ] -> [ Settings ] -> [ Connections ] -> [ Wi-Fi ] -> [ Network Adapters ]) and choose "Work" from the combo-list box labeled "My network card connects to:".
For some screenshots:
"Open Path" menu in File Explorer keeps showing "Cannot Connect" message.
http://choung.net/handbooks/SharePlug/troubleshooting