Thanks for the replies !

Just to come back on the below feedback:
- Caps are used to stabilize power supply (100nf and 10mf) and also every PIC has a 100nf cap on the power supply pin
- MCLR has a pull-up resistor
- LVP set to off

Other ideas what it could be?

I can post the network drawing (Eagle file) but i'm not sure if i can attach files ...

Many thanks for helping me with this !!

Wilbert