This is a common problem with some verions of the JDM programmer. There is a fix that is shown below.
Full details of this modification can be found at http://users.tpg.com.au/btkelly/jdm_b.htm
Another version can be found at http://www.janson-soft.de/pic/pic.htm
I use a commercial version of the JDM programmer from Olimex
which is based on the following schematic
Hope this helps
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