In case you get something along the lines of
$ formchk input.chk output.fchk Read checkpoint file input.chk Write formatted file output.fchk Missing data for FChkPn. Error termination via Lnk1e at <DATE> Segmentation fault
this means that your checkpoint file (*.chk) is damaged. Please make sure, that ...
- ... you have enough space available to actually store the whole checkpoint file
- ... Gaussian09 did not crash during the simulation that produced the checkpoint file
- ... the geometry optimization converged (if this is applicable)
- ... you use the same Gaussian09 binaries that have been used for checkpoint file creation, as the normal checkpoint file format is both version and architecture dependent.