I saw this error on android when using the sample tutorial code from jexcelapi site. For example, http://www.andykhan.com/jexcelapi/tutorial.html
The fix for me was to replace CellType on the right side of the cell comparison:
For example, change:
if(a1.getType() == CellType.LABEL)
For this:
if(a1.getType() == cell.LABEL)
If the cell is filled with a .getCell (...) api sheet:
Cell cell = sheet.getCell(j, i);
Hope this helps!