extract from pickit2 user guide.
If a short or heavy current load is detected on the PICkit™ 2 Microcontroller Programmer supplied VDD, then the user will receive an error as in Figure 2-6 and VDD will be automatically disabled.
To avoid heavy current load errors, it is recommended to keep the target current consumption below 25 mA. Large VDD capacitances should also be avoided as they slow down the VDD risetime. The allowed VDD rise time is 500 μs or less.
after this extract from an old pickit2 user guide, you can understand that the electrolytic caps should have lower value.
then, what is the inductor that you have used?
is it definitely above 500uH. if not this Vpp problem would arise. for low Vpp error, check Q6,7and 8 whether they are proper in type and mounting.
also the MosFets(Bill advised you that they are not that important and gave a suggestion how to avoid them for the time being.
many a time these Q6,7and 8 skip observation. the best would be to remove them all together. place fresh ones. . never replace a device because earlier so and so was there. a mistake done at the beginning, would be repeated. then, if you use other than 2n23904 and 3906 that follow EBC order, judge the pins order as per the device you use. For example BC547 and 557 follow CBE order as against 2n390x.
the electrolytic capacitors can better be tantalum caps instead of cheap ones that might be some times leaky.check whether the 4k7 and 2k7 chain after the diode D4 is proper and not reverse. of course i am also getting similar message of Vdd on a full version assembled and trying to debug it.
carefully record your observations and post
PS: A fully assembled pickit2 draws 46mA as it is powered. later it will draw more as the software functions and Vpp generation is ON etc, Even If the voltage is correct at 5V DC at USB, there is no wonder that 18F25450 becomes slightly warm.