Is it true that lccorr is unreliable?

Yes. During the scientific validation of SAS 6.5.0 serious problems with the EPIC light curve background subtraction and exposure correction task lccorr were found. As a consequence of this, the task was not distributed with SAS 6.5.0 and this was documented in the release notes.

Due to an oversight the task was re-introduced in version 7.0.0, before solution of the main issues of concern. While in some cases lccorr is working, in many others it produces segmentation faults, which are most probably due to memory leaks. Since this could affect the results without the user noticing, we discourage the use of lccorr until a full scientific validation of a repaired version (currently underway) has taken place.

Instead we recommend to use the ftools task "lcmath", taking carefully into acount the advice given in a previous watchout item:

• Artifacts in XMM-Newton time series analysis? -- Answer