For nortal (avtive: BTN/PASBTN) icons use path:
ReplaceableTextures\CommndButtons\BTNyour_icon.blp
You need also disabled icon of normal icon you are using, becasue without it, icon will appear as green in some cases. Egzamples when disabled icons appear: you dont have requirements for upgrade/unit/ability or you have clicked Menu (F10).
For disabled (DISBTN/DISPASBTN) icons path is:
ReplaceableTextures\CommandButtonsDisabled\DISBTNyour_icon.blp
So basicaly: 2 icons per 1 proper import.
EDIT: WHAT HAVE YOU IMPORTED?
Post map in pastebin with link, or just post map here. I dont understand how after importing simple blp texture something like this happened. Have you been changing anything besides this in your map?