Gmax does not support support .BMP with an alpha channel?

Really strange,I apply an BMP with the alpha channel to the material ball,in the first time,there's no problem in doning this.After that I rebooted my computer and ran GMAX again,when I use the .bmp with the alpha channel again,the GMAX reported that the BMP is not supported?And the .BMP without the alpha channel is just fine with GMAXBTW,I created the alpha BMP in photoshop,by using the saving option "depth:32 bit" and "format:windows"