Options - Preferences - Close media files when not the active application. When this check box is selected, files can be edited in external editors (audio, image, etc.) while they are contained in events on the Vegas timeline.
Or go to Rosebud's site and grab his excellent Open In Graphic Editor script.
when it occurs, vegas puts the psd offline and will not even let me re import it. i then have to change the name of the file from photoshop or remove the file from the project media bin and re-import it into the project.
Works fine here.
I am currently working on a "Marauder's Map" effect and I have over 100 tracks imported from one PSD file.
I opened a new Vegas (10e) project, dragged the Photoshop PSD file into the timeline - across tracks. Opened the same PSD file and made a change on one of the layers and saved the PSD file. In Vegas, the changes I made appeared in the Vegas project.
It didn't matter where the cursor was in Vegas. I did it twice.
Are you sure the file isn't open somewhere else?
Have you tried removing unused media from the Project Media window?