Easy2Boot v1.42+ has a new feature that means that you don't have to make all your linux ISO files contiguous (though it will be much faster if you do!).
This feature is mainly for linux users who may have difficulty in defragging the E2B payload files, due to the lack of linux defrag/contig utilities.
If the ISO is not contiguus, E2B will copy the contents of the whole ISO to the \_ISO\CONTIG.ISO file which is a contiguous file. E2B will then boot from CONTIG.ISO instead of the original ISO file.
However, this feature is only useful for .ISO files that are reasonably small as it takes time for E2B to make a contiguous copy of the ISO (and it does this each and every time you run the same ISO).
E2B already contains a 500MB CONTIG.ISO file. You should ensure this file is contiguous as soon as you have made the E2B USB drive.
If you are short of space, you can just delete the CONTIG.ISO file (but you then cannot use this feature).
If some of your ISOs are larger than 500MB, you can make a larger CONTIG.ISO file. It does not matter what is in the CONTIG.ISO file, as long as it is contiguous and is the same size or larger than the non-contiguous ISO that you are trying to boot from.
If you see this message:
WARNING: /_ISO/CONTIG.ISO is smaller than ()/_ISO/xxx/yyy.iso - cannot copy!

then you will need to increase the size of the CONTIG.ISO file or make the source ISO file contiguous (e.g. using WinContig or Defraggler).
The CONTIG.ISO file must be at least as large as the ISO file you are trying to boot from (max 4GB) .
Note that the copy process can be quite slow on some systems or USB Flash drives - this copy time can often be greatly improved by using the 'Install Grub4DOS USB driver' menu option first (in the Utilities Menu in later versions), before you select the ISO file. This option is only visible if grub4dos 0.4.6a is in use (default).
To enable this feature, simply ensure that a large contiguous \_ISO\CONTIG.ISO file exists...
  1. Copy a large file - e.g. 3.8GB, to the \_ISO folder of your E2B USB drive and rename it as CONTIG.ISO. Any file will work as long as it is larger than the largest ISO that you might use (up to 3.9GB). You can create a large file using the RMPrepUSB - Create Ext2 FS button if you wish.
  2. Then run WinContig on the E2B USB drive to make sure that the CONTIG.ISO file is contiguous (or use DeFraggler or WinContig just on the \_ISO\CONTIG.ISO file).
Now when you add any new linux ISO files, if you forget to make them contiguous, E2B will copy the ISO file to CONTIG.ISO and boot from that file.
For more details see my blog post here.
Note: Do not exceed 3.99GB for the CONTIG.ISO file (even on an NTFS E2B drive) as the size check in E2B will not fail due to a grub4dos bug.
Tip: To boot to grub4dos 0.4.6a and load the USB driver, add a \_ISO\MyE2B.cfg file by copying the Sample_MyE2B.cfg file and uncomment the line 'set GRUB_USB=Y' to automatically load the 0.4.6a USB driver when E2B loads (note that this may cause problems on some systems!). You can hold the SHIFT key down as E2B starts to boot to load the USB driver too.