This means that the eventrate file, which is used to calculate dead times, contains no data for nn timebins.
"Warning: bad eventrate data for nn timebins"
This means that the eventrate file contains a silly value for the number of events recorded by the detector in a given time bin. This number can either be zero, negative or ridiculously high.
Both of these messages suggest some problem with the eventrate, *_EVR, file. The dead time correction is typically only about 3 percent, so unless you are interested in very accurate time series work, these messages can be safely ignored. It may be better to perform the corrections again with the dead time correction turned off by putting DCORR=NO on the command line.