I have been running this command virtually all day -
C:\Users\Dad\Desktop\oclHashcat-2.01>oclHashcat64.exe --session md5 --show -o found.txt --outfile-format 2 "C:\Users\Dad\AppData\Local\Temp\tmp7C41.tmp"

until now - Hashcat keeps crashing

Problem signature:
  Problem Event Name: APPCRASH
  Application Name: oclHashcat64.exe
  Application Version:
  Application Timestamp: 5662d84a
  Fault Module Name: oclHashcat64.exe
  Fault Module Version:
  Fault Module Timestamp: 5662d84a
  Exception Code: c0000005
  Exception Offset: 00000000000265b6
  OS Version: 6.1.7601.
  Locale ID: 2057
  Additional Information 1: 26be
  Additional Information 2: 26beb5d19cd34020aa30840c1df8ad6b
  Additional Information 3: c306
  Additional Information 4: c3069e329b5cdefa8c7b46b9f26f6728

At first I thought it was because of the size of the file 561,000 hashes so I reduced the amount 319 as in the tmp file above.  oclHashcat runs fine using the Hashcat Gui and is running the 561,000 hashes now but I cannot access the pot file with the --show command without it crashing on the command line.

Any ideas/help?
It seems to be a problem with the md5 pot file as two other pots seem to work fine without it crashing so I am going to delete/rename/rebuild the md5 pot and see if there is a difference
I may have resolved the issue - it appears that the md5.pot file may have become corrupt. I have subsequently deleted it and created another one using hashcat. This appears to have sorted the problem for now but will know for sure after some further testing.

Thanks to all those who took the time to read this thread.