Finding method def for error signature on Windows XP SP3 PC

Question

I am trying to find the System.dll file to open with ILDASM.exe and find the method definition and offset and see why my application is crashing on Windows XP machines only. Am I trying to open the correct dll for this assembly listed in this error signature? I'm looking in C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\v3.5 at System.Core.dll because it has the System namespace in it when opened by ILDASM.exe.

The same program runs just fine on a windows 7 PC.

I have the following Error signature from attempting to run my application on a Windows XP machine with service pack 3.

Error signature
  EventType: clr20r3
  P1: myapplication.exe                 >Is the exe file name
  P2: 1.0.0.0                           >Is the exe file assembly version number
  P3: 51e6a3d8                          >Is the exe file stamp
  P4: system                            >Is the faulting assembly full name
  P5: 4.0.0.0                           >Is the faulting assembly version
  P6: 5073c71b                          >Is the faulting assembly timestamp
  P7: 3d57                              >Is the faulting assembly method def
  P8: bd                                >Is faulting method IL Offset within the faulting method
  P9: system.invalidoperationexception  >Exception type that was thrown