Answer for Cant save to ext. HDD

Was this drive formatted NTFS either by you or from the factory? If so, that’s why you can’t write to it from the Mac. OS X can read an NTFS drive but cannot write to one. To use the drive on the Mac do this:
 
Drive Preparation
 
1. Open Disk Utility in your Utilities folder.
 
2. After DU loads select your hard drive (this is the entry with the mfgr.’s ID and size) from the left side list. Click on thePartition tab in the DU main window.
 
3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Optionsbutton, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed.
 
4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erasetab in the DU main window.
 
5. Set the format type to Mac OS Extended (Journaled.) Click on the Security button, check the button for Zero Data and click on OK to return to the Erase window.
 
6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.