I am not sure why you get that error. I have lots to learn so one of the more knowledgeable people out here will need to answer the why question.

I did match my code that works with yours and except for an element name and an extra variable they seemed the same so I took your code and  put it into my working example and found that I had to replace all the cust# with cu# and it works fine. I get no errors.

Try replacing your code with this. If your element is cust# instead of Cu# change them back as needed.

Keep us posted!

var vAllCustomers as String
var vAllCustNos as String
var vCompany as String
var vCompanies as String
var vCnt as Int
If Cu# <> "" Then
{
If @XLookup(@Fn, Cu#, "Customers!Customer #",
"Customer #") <> "" Then
{
vCompany = @XLookup(@Fn, Cu#,
"Customers!Customer #", "Company")
vCompanies = vCompanies + vCompany + ";"
vCnt += 1
}
Else
{
vAllCustomers = @XListValues(@Fn,
"Customers!Company")
While @Len(vAllCustomers) > 0
{
vCompany = Split(vAllCustomers, ";")
If @Left(vCompany, @Len(Cu#)) = Cu# Then
{
vCompanies = vCompanies + vCompany + ";"
vCnt += 1
}
}
}
If vCnt > 0 Then
{
vCompanies = @Repllas(vCompanies, ";", "")
Company = @PopUpMenu(vCompanies,"SELECT
CUSTOMER" + @NewLine() + "FOR THIS INVOICE")
If Company <> "" Then
{
Cu# = @XLookup(@Fn, Company, "Customers!
Company", "Customer #")
Name = @XLookup(@Fn, Company, "Customers!
Company", "Name")
Address = @XLookup(@Fn, Company, "Customers!
Company", "Address")
City = @XLookup(@Fn, Company, "Customers!
Company", "City")
State = @XLookup(@Fn, Company, "Customers!
Company", "State")
Zip = @XLookup(@Fn, Company, "Customers!
Company", "Zip")
}
}
Else
{
@Msgbox("No companies found that begin with &#8216;"
+ Cu# + "&#8216;","","")
}
}
If Cu# = "" Then
{
vAllCustomers = @XListValues(@Fn, "Customers!
Company")
Company = @PopupMenu(vAllCustomers, "SELECT
CUSTOMER" + @NewLine() + "FOR THIS INVOICE")
If Company <> "" Then
{
Cu# = @XLookup(@Fn, Company, "Customers!
Company", "Customer #")
Name = @XLookup(@Fn, Company, "Customers!
Company", "Name")
Address = @XLookup(@Fn, Company, "Customers!
Company", "Address")
City = @XLookup(@Fn, Company, "Customers!
Company", "City")
State = @XLookup(@Fn, Company, "Customers!
Company", "State")
Zip = @XLookup(@Fn, Company, "Customers!
Company", "Zip")
}
}

If Company <> "" Then
If Invoice# = "" Then

{

Invoice# = @Number
Invoicedate = @Date

}

Thanks! 

I thought I checked and double checked my names - but that was the problem.

Thank you.