Been using microchip's LPC (low pin count) curiosity board that came with a PIC16F18446. Out of the blue my program does not seem to be uploading to the pic and I'm greeted with the following under the PKob4 tab:

"
Transmission on endpoint 2 failed

Failed to get Device ID. Please make sure the target device is attached and try the operation again.
Connection Failed.
Transmission on endpoint 2 failed
"

I'm using MPLAB X IDE v5.40 and the curiosity board's on board programmer (PKoB4) as the programmer. My program is not the issue as I have been uploading to this pic and board many times working on a project. I'm absolutely baffled as to why this is happening and must fix it as soon as possible. Can anyone help?

 

Assuming that you haven't smoked the board try this:
Be sure the USB cable is good and the power LED is on.
Disconnect the LPC board.
In Project Properties, select another USB debugger like PICKit 2, 3 or RealICE.
Click Apply and close the window.
Click Debug Start to rebuild and make it look for a different device. It won't find one.
Close MPLABX.
Reopen MPLABX
In Project Properties reselect the LPC debugger.
Click Apply
Reconnect the LPC board.
It should find it and be ready to go.

I don't know if that will solve your specific problem. It is a shotgun approach that I have used in earlier versions to force it to look for another USB driver then reload the one you want.

FWIW Ver 5.40 is a big change from earlier MPLABX. There may be bugs we don't know about. I did bring up 5.40 with the Curiosity LPC and it found it when I selected it as the debugging tool. I normally use 5.10 with the older PKOB.
Make sure MCLR is high on the target chip and that you have left Low Voltage Programming enabled in the config bits.
Sorry I don't have more for you.
Good luck!