Updating fields within a database

When writing a text box that is empty to a database field the error 'Errors Occured' is generated by the application. The only way I can get by this is to use the 'Cstr' function around the textbox. This however does not always work. What am I doing wrong?? Please help.

what type of field are you writing to?

if you try to save string data (using cstr) to, say, an integer field - you're gonna run into all sorts of problems