A table can have up to 255 'fields'. A range attribute consists of two fields (the upper and lower limits). Therefore if a table contained only 'range' attributes, the maximum number of attributes permitted is 127. If a table contained only 'discrete' attributes, then the maximum number of attributes is 255.
If CES Constructor warns you that you cannot add more attributes, compact the database and try again. You can find this option in the Tools menu at the top of the screen by selecting Check and repair.
If you want more than 255 attributes, please contact sales@grantadesign.com.