Bueno, usando san GOOGLE, encontre esto en una
PAGE, en donde te dirigen a la pagina oficial de
AMFPHP, en donde habla sobre ese problema en el siguiente parrafo:
BOM headers in Unicode files cause corrupt output
BOM headers in your service files may cause the output stream to become corrupt. That is because the output stream will contain the BOM header which is not valid AMF. Although in 99% of cases the BOM headers will not cause issues, some combinations of PHP version and server version and possibly the alignment of Jupiter may cause this rather nasty problem to show up. The solution is either to save as ASCII or to save as Unicode in an editor that doesn't add a BOM header, and deleting the old BOM header with an hex editor. UltraEdit in particular will do the job. To verify if this is indeed happening, load up Charles or Service Capture. If you see an error like 'cannot modify header information, output started at (guilty file):line number', then you've found the source of the error. Resave as DOS or Unix ASCII and it should work fine.
En resumen dice que los headers no causan problemas, pero que podrian causarlos debido a ciertas versiones de PHP, el servidor y la alineacion con jupiter

Ahi dice que necesitas guardar todo en codificacion ASCII, o guardarlo en UNICODE en un editor que no genere BOM headers, ademas deberias borrar el BOM header que ya estaba con
UltraEdit,

ese no es gratuito, pero es el que recomiendan. Yo sigo pensando que tienes por ahi un espacio en blanco, Suerte.