Global parameters deleted instead of read

If I put this into a custom node, the global parameters are actually deleted from my project after i ran it. But it should rather read the global parameters. The python script is just a simple if statement:

ibboxh = IN[0]
ibboxv = IN[1]
ibbox = IN[2]
aOutput =[]
# Place your code below this line

if ibboxh > 0 and ibboxv > 0:
	ibboxhdef = ibboxh
	ibboxvdef = ibboxv
	ibboxhdef = ibbox
	ibboxvdef = ibbox
# Assign your output to the OUT variable.
OUT = aOutput

anybody an idea why it deletes this parameters?