Hi
Unfortunately i cant help with this over the web, a problem like this requires sitting in front of NAV and tracing transactions, use the navigate to figure out where the original transaction comes from, check every part of it against a posting made manually in an un-customized cronos system and look for differences
I have found many problems relating to journals in the past and all of them had to be resolved by tracing transactions, some of the things that i found,
Currency, you mentioned that you do not use currencies, however make sure that there are not some transactions with a blank currency code and some with the local currency, even though both mean local they are still different currencies
Migration, this is the biggest, how were the go live entries created, were they brought in via a journal, what journal was used, were they manually typed in or data/xml port, were any of the posting code units modified, the answers to these questions could mean that not all the financial rules were applied and then you end up with a recon nightmare
Applications, have all applications been done using NAV forms or is there any kind of automation / integration
New records, same as above
The common theme of this is that NAV standard works really well, when there is a strange problem it is normally as a result of a Automated migration of data / development / customization, for this reason the first place you should look is at customization, and try the transactions in a standard system with manually created transactions and look for differences and as a separate exersize always avoid customizing anything that has an impact on posting
Hope this helps you get to the bottom of the problem
Cheers
Nev