Object Reference is not compatible with Self Object Reference

[etretableau1 (etretableau)]

I’m new to Bluprints and try to compile a simple blueprint using ‘Array’.
When i try to connect to ‘Array Element’ to target in ‘Move Forward’ function, I keep getting message “Object Reference is not compatible with Self Object Reference”
What does it mean? What’s wrong with it?

Thank for your help!

[ClockworkOcean]

Just delete the move forward node, and make a new one by dragging off the loop ‘array element’ pin.