*** Warning: CYCLE not found or invalid in /tmp/imap_3.fits --- assuming 'P'
The CIAO response tools will issue this warning if the CYCLE keyword is missing from the file header. The CYCLE keyword is needed in alternating mode observations (also referred to as interleaved mode) to indicate which frame time was used in the file. If you are not working with interleaved data, you can ignore the warning.
The What is the CYCLE keyword? FAQ explains further about this keyword.