For me it is usually accessing a mapped drive letter instead of UNC paths. Try loggin in as the user who Data Pump runs in as, unmap any network drives, and try to walk through the process manually. Look for an error message that pops up.
By the way, when you call your .bat file from a script make sure you return false if it times out, and send a notification to yourself.
You should also check the task manager to see if you have any hanging MSACCESS threads that need to be killed.
Your macros do have a quit at the end to close Access at the end, correct? You set warnings to be off at the beginning of the macro?
One other thought - with Access 2007, do you need to log in as the user and change the securities so Macros are enabled?
Just a few ideas.