Image maxsize problem

Hi,
I was trying to set maxSize in config.asp like,

Set ResourceTypes(1) = DefineResourceType( _
"Images", _
baseUrl & "images", _
baseDir & "images", _
"1M", _
"bmp,gif,jpeg,jpg,png", _
"" _
)

and it still uploads file having size of 1.24 MB.

I tried to set

Set ResourceTypes(1) = DefineResourceType( _
"Images", _
baseUrl & "images", _
baseDir & "images", _
"500K", _
"bmp,gif,jpeg,jpg,png", _
"" _
)

and I tried to upload 860K size file and it didn't upload. So there it worked fine.
Then again when I tried 1.24M size file , it uploaded.

I am not getting why it is acting this way.

can somebody help me here?