I noticed I try to use an orthorectified image, which is my mistake. FLAASH works with the unorthorectified one.

FLAASH will also work on the orthorectified result. The error you received has to do with all the additional background (blank space) that is created after ASTER is orthorectified. What happens is because the image is large, it must tile the processing and it is grabbing a tile that has no data in it. You can probably get around this error by increasing the tile size in the FLAASH Advanced parameters from the default of 100mb to200mb, or perhaps more. Hopefully this will be enough to grab some of the actual data. Sometimes, for very large images with a lot of background, it can be difficult to make the tile size large enough without running out of contiguous system memory, which will then trigger a memory allocation error. In these cases, it is sometimes necessary to subset the images when processing in FLAASH.