No, this error normally means that you are trying to convert values that are not an actual date.
11/31/03, or 2/29/2003, or 13/05/04, for example.
This happens when you have a database that does not store values in datetime format. It can also happen if you supply a day, month, and year value to SQL server in 2-digit formats and SQL server is unsure which value represents which part of the the date.
What code are you using for your conversion? You could wrap the ISDATE() function around it and query against your source table to find any values that it cannot convert.
If it's not practically useful, then it's practically useless.