Click on one of the view toggles along the bottom of raster manager to toggle the display of attached image on in a view and it stays grey (off) instead of turning blue (on).
Along the bottom of Raster Manager are 8 button labled 1-8. These are the 8 views that can be used in Microstation. For example if the button labeled with 1 is grey then the attached raster image will not display in view 1. If it is blue the image will display in view 1. Simple click on the button to toggle the display on/off for that view. If the button stays grey or turns a darker shade of grey this means the level the image is on has it's display turned off.
Starting in XM images are placed on levels when attached. By default they attach to the active level. If this level's display is ever turned off then the image will not display. In raster manager double click on the image name and the element information dialog will come up. Here check the General section for the Level the image is on. In Micrstation go to settings - levels - manager and turn the display of the level on. You can also change the image to a different level in the General section if the level needs to stay off.
Also see the following article for more in depth information regarding images and levels in Microstation XM and V8i.