I'm assuming that the file from Emdeon (yes... we use them too) is your input file and that the W:\ is a mapped drive to a network resource. Either that or your server has a LOT of local drives on it. What I'd try first is to use the UNC pathway that W:\ is mapped to because I've ran into problems before when using mapped drives. Also, make sure that the credentials the DataPump service is running under has the proper rights to the network resouce. Open the Services MMC under Adminstrative Tools and check what the service "Monarch DataPump 10" is using.
Although you can specify different credentials for Windows to use when mapping a drive rather than what the server or pc is signed into Windows with, DataPump is going to use whatever credentials its service is running on. If you used the default setup when you, or whoever, installed DataPump, more than likely DataPump is using the local system account, which may or may not have access to your resource. If this is the case and you decide to change what credentials DataPump runs under, make certain that the credentials you use doesn't break other processes' rights to their resouces.
Hope this leads you in the right direction.
Perhaps the projects all point to UNC paths
server\share\folder\file but this error is coming instead from an external lookup in a model file? If you edited the model on a desktop machine perhaps you connected the lookup using W:\...\. Monarch Utility will help you double check this.