First you need to take a deep breath.  You cashed a check from an unknown source and even though you did it unknowingly as to the fraud, you can still be charged.  But yes, you cal definitely plead "not guilty" and you should with an ATTORNEY by your side.  You are entitled to one appointed by the courts but I would consult with a private attorney as well.  DO NOT GO TO COURT ALONE. There could be deals made here as to the parties really responsible that could help reduce or dismiss the charges.  Please.