For anyone like me who has dumped their jasper 512 with nandpro with only the flash portion and can't extract with ibuild heres a quick fix. My original dump was 68.0 MB (71,368,704 bytes) in size but the goal is 66.0 MB (69,206,016 bytes). Make a backup of your file before going forward. Open the one you plan on using in a hex editor and make sure the ruler is extended to 2b.

now click edit and choose goto, in a hex format paste 041fffd4. Make sure everything beyond this point is null (FF). Once you confirm, highlight from the row directly under ( so from 0420000 on)

all the way to the end and hit delete. Save the new file and confirm the new size is 66.0 MB (69,206,016 bytes)

Throw the new file through ibuild and everything should extract fine now.
sorry for the pic sizes
You can also use nandpro to make it the correct file size by "nandpro <original file name>.bin: -r64 <new file name>.bin" example: "nandpro originalnand.bin: -r64 66mbnand.bin" Much easier than having to hex edit anything.