Gaussian09: formchk error message

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.