Linetype shape files keep disappearing

I have a custom linetype (fma.lin) and a custom compiled shape file (fmashp.shx) that is being used by my linetype file. I can load the linetypes and shape files and eveything works great. However once I switch files, or create a new one and come back to the previous drawing my shape files are gone in my linetypes. I have to load the shape file and reload the linetypes and they usually return. This has even occured with xrefs and most recently I have been unable to make them reappear in some of my files. If I check the purge option it shows that the "fmashp.shx" file is not in use, but if I check the items in use it shows the "fmashp" file is in use. Confused and relly need some help. Thanks. Also Im running Land Desktop 2009 but have had this issue with 2008.