VB.NET - What is the reason of this error in Crystal Reports?

I have a problem with the crystal reports.I have a report in which four tables are bound as source to the tables.In those 4 tables one table database fields are used in the formula fields.When I set that formula field on the report I am getting error this error "Unknown Database Connector Error" in the Preview Report.

Suppose when I remove that field or comment the formula code of that field we are not suppose to get that error.I don't understand that error too.

I have written like this in the formula field

 
if{students.name} = "" then 
else
 "Student Name : " + {students.name}

I have googled alot but no use.Can any one help me regarding this ?

try to avoid write the code while create the report...SELECT FROM THE FIELD AND AUTO CODE WILL BE genarate

I have created the Report and setting the data programmatically to the table.

When I run the same report in other machine am not getting that error in design time and runtime also.