I have about 6gb on my laptop but have an external hard drive it has 200gb free but is only USB. I have tried this but keep getting the same error. Is this because it is USB?
Using a USB drive would probably not generate this particular error. I do, however, recommend use of a firewire hard drive interface where large files are concerned and high throughput consistency is demanded (e.g., with DV capture without dropped frames). In this case, it is most likely that your "large" file output/sharing is using all available space on your start-up drive which is why I told you to get rid of any files that aren't needed. (For instance, are your project "source" files located n the "start-up drive or your external USB drive?) One basic "rule of thumb" is to have 3 times as much space available on your start-up as is required for your source file if working exclusively on the start-up drive before even beginning your project. This, of course, assumes that you are following a secondary "rule of thumb" which implies that each stage of your editing work flow progresses from one compression format to another of equal or more compression.
For example, lets say want to import an SD 13 GB DV compressed source file for editing in iMovie '08. By this rule I would like to have about 39 GBs available before even starting my project. When I am finished editing lets say I want to export the content as an AIC/AIFF file for chaptering and audio work in GarageBand. This will likely produce a second file on the order of 9-10 GBs. When done in GarageBand, I decided to "send" the data to iDVD which does not significantly increase my file size since the chapter track is a text track of very small size and the PCM audio is already prepared for multiplexing in iDVD. At this point iDVD will take my GarageBand data and convert the video to M2V and multiplex it with the PCM to create VOB files on the order of 3-4 GBs. Thus, the total hard drive space used for my projects using this work flow was about 13GBs + 9-10GBs + 3-4GBs or a total of 25-27GBs which doesn't include any temporary caching the various applications may need during processing.
In addition, certain sharing/exporting work flows create duplicate files which may be stored on your start-up drive and about which you should be aware. For instance, if you share an iMovie project to iTunes, one copy is stored in the start-up drive named_Project package files, a second is stored in your "iMovie Sharing > iTunes" folder on your start-up drive and, if your iTunes preference is still defaulted to "copy" files to the iTunes library, a third copy of your project output would be stored in the iTunes library on either your start-up or external drive as you specify. As you can see, it is often easy to "use" more hard drive space than you realize when working in iMovie. My best guess is that your "long" project export is eating up your entire 6GBs of free space between the creating of output files and the use of temporary caching performed in support of the creating of these shared/exported files.
