The following are some error messages which might be encountered in the normal course of program operation:
Too many lines of descent / too many children in 1 generation
Links mismatch: extra line of descent needed to accommodate cousin marriage?
Manual editing required, name cannot be truncated automatically
Title font too large: title wider than page
There are many other error messages, and their occurrence may indicate problems with the data. Problems could be caused by missing data, or by incomplete, inconsistent or otherwise unusual data. The author has experience of one GEDCOM file in which an individual makes an appearance as her own great grandmother, causing problems. Note also that it may not be possible to produce a selective tree where there is a complex conjunction of cousin marriages.