This means that the "Unmanaged Disk" destination has not been "turned" on for your system. This has to be done in two places in the Central Management Console (CMC).
1. Log in to the CMC and click on "Servers". The list of services will come up.
2. Click on "Destination Server". Go to the "Destinations" tab, check "Unmanaged Disk" and then click on the Enable button.
3. Repeat step 2 for each "Crystal Reports Job Server" (you will have one or more.)
You say that you are scheduling to a "mapped" drive. Is that drive mapped on your local computer or on the report server? The reports run on the server and know nothing about what's on your local machine. So, if the mapped drive is mapped from your workstation, you'll need to save to a UNC file path. Also, the user account that is running the report services MUST have access to write the file to the folder unless you specify that it log in as another (network) user when saving the file.
-Dell
A computer only does what you actually told it to do - not what you thought you told it to do.