Error in delay calculation

hi all,

I've got  an error while calculating delay using delay function in virtuoso.

the error is : p, li { white-space: pre-wra"(\"plus\" 0 t nil (\"*Error* plus: can't handle (nil + 0.0)\"))"Expression "delay(?wf1 v(\"/X1\" ?result \"tran-tran\"), ?value1 2.5, ?edge1 \"either\", ?nth1 1, ?td1 0.0, ?wf2 v(\"/sum\" ?result \"tran-tran\"), ?value2 2.5, ?edge2 \"either\", ?nth2 1, ?td2 0.0 , ?stop nil, ?multiple nil)" does not evaluate to waveform."

i couldn't figure out what was the error. Please help..

 Virtuoso version: IC6.1.5.72