I want to write a PCF do find a new high for IPOs.  If I scan a time period that exceeds the number of days a new issue has traded I get  a null value in my column.  How can I write a formula that will get around this issue

You can't create a formula that gets around this issue. In TC2000 version 12.3, you could click on Price History and select Create Scan Condition to create a Condition for a New High, but there is no way to do anything similar in TC2000 version 7.