It's quite possible that the symbol is preventing you from accomplishing your astral projections because "you already believe that it could negatively impact your spiritual growth". Once the seed/thought has been planted, whether or not it may have actual power or not, your subconscious is still going to see it as a negative and your attempts to project will be hampered.

I was thinking along the lines of worldwatcher, although I initially didn't post because I don't believe I'm qualified (I haven't successfully left my body yet)

All I know is any negative thought could hamper your ability to get into the state required to leave the body.

[edit on 18/5/09 by dmorgan]

I tried to project last night before I went to sleep after not wearing the medallion for 24hours, It was a strange sensation...as though I have been weakened like trying to lift something you know you should be able to but just cant! I tried and tried and eventually fell asleep. I will however, be trying again in around 20-30mins when I retire to bed. Ill post updates tomorrow and let you all know how I went.
-Tim.