Look like at time import book, you have time out error. You may check that if set "Error Reporting" to Max in yours books site "Global Configuration"
If that true, most simply way:
- or do full back up, run site at local PC. On Local PC set time mout so much - as need - and do import
- or you may do import with help database
- or need go to script - and try high "script execute time" - but some time from script impossible change that value
May I just change the IDs in the importing CSV file for ex. 4001...4005?