.bitmap is a tool compiled format. What you need to do is compile it in tool using...

tool bitmap file_location


For example...

tool bitmaps levels\b30\bitmaps

...would compile the bitmaps in that folder


to compile 1 bitmap at a time for example (in this case being cliffs.tif)...

tool bitmap levels\b30\bitmaps\cliffs


With this I hope you are able to figure this all out.

Setting your bitmap to explicit alpha is not going to help it because the error is appearing because its dimensions are not a power of 2.
Powers of 2:
2
4
8
16
32
64
128
256
512
1024
2048
4096
etc...

your bitmap must be something like: 512 x 512 in order for tool to compile it.

power of two basically means bitmaps with the dimensions of two... well... to the power of some number.
anyway...
examples of possible sides are as follows

2 = 2
2 x 2 = 4
2 x 2 x 2 = 8
2 x 2 x 2 x 2 = 16
and so on and so forth.

2
4
8
16
32
64
128
256
512
1024
2048 ( which is the highest that halo supports I think )


EDIT:

does halo support 4096?
Edited by eliteslasher on Jan 30, 2011 at 03:07 AM