"-36" error message using Acomdata...

Question

Have a new Acomdata 500 GB External HD. Using it with an eMac 1.42 GHz PowerPC G4 with 512 MB DDR SDRAM. Seem to have installed it properly, then began trying to move movie files. Several files moved properly, but since then all I get is a "-36" error message. My Mac is in desperate need of moving these files to the EXTERNAL, to free up memory. These movie files are chewing up space. But what's with the Acomdata? And the error message? And how to fix???