Large list in data validation produces error when sheet opens

[Louis . Masters]

I'm running into an issue when I put a large number of items(>25) in the 
data validation list.  My code:

                prompt = truncateString(prompt,250,true);  //excel limits 
to ~255
                validationMsg = truncateString(validationMsg,250,true); 
//excel limits to ~255
 
                org.apache.poi.ss.util.CellRangeAddressList addressList = 
new org.apache.poi.ss.util.CellRangeAddressList(firstRow,  lastRow, 
firstCol, lastCol);
                constraint = 
validationHelper.createExplicitListConstraint(valList);  //BOOM
                dataValidation = 
validationHelper.createValidation(constraint, addressList);
                dataValidation.setSuppressDropDownArrow(true);
                dataValidation.createPromptBox("Valid Values", prompt);
                dataValidation.setShowPromptBox(true);
                dataValidation.setShowErrorBox(true);
 dataValidation.setErrorStyle(DataValidation.ErrorStyle.WARNING);
                dataValidation.createErrorBox("Validation Error", 
validationMsg);

                sheet.addValidationData(dataValidation);

When the sheet opens, I get a generic error message about a problem with 
the sheet.  When I click to go on, it removes the validation and opens as 
normal.

I tried removing the prompt box, but the issue still occurs.

POI 3.7 on Win, jdk 1.5

Any ideas?

-Lou