I know maya dose not like name spaces (eg d:\work 3d\ - would be bad but d:\work3d\ - would be better) so try moving the files/renaming them.
Also unless your image seq is very sort I think the numbering will also have to change from (1) to something more like 001 with out the brackets as Maya will need to 0`s to read the sequence in the right ordered and maybe the reason its throwing up the error.
So try moving the files and rename them from
D:/My Documents/maya/projects/Apache Helicopter/sourceimages/Fire/Fire (1).png
to something like
D:/Helicopter/Fire0001.png
and see if you still get the errors. If that dont work try a different file type.
Hope it helps.
Last edited by tweetytunes; 16-07-2011 at 09:14 AM.