Forbidden data in a Data Grid?

[Paul Looney]

Are there characters that prevent a Data Grid from displaying?

We have Data Grid in the UI front end to a database.
For years it has worked well with databases for many different customers.
Recently the data from one customer would not display. Stepping through the code, all was well until the end - setting the dgtext of the data grid. The scroll bars resized properly. The number or records listed was right. Clicking on a line in the Data Grid opened the record viewer. 
But no data was displayed in the Data Grid fields.

The same grid continued to work with data from other customers. That customer's data was visible in other grids.

It is just that this one grid will not display data from this one account.

We already strip out NULLs (from our experience with sorting problems) but are there other characters that would cause a Data Grid to not display data?

Or should we look elsewhere?

Thanks in advance,
Paul Looney