When transferring 4D files over the network from one Mac machine to another Mac machine, there are two protocols that are normally used; SMB and AFP.

If the database was natively created with 4D 2004, meaning that the structure and data file were not upgraded from previous versions, using either protocol to send the files over the network will not harm the integrity of the files. On the other hand, if the database was upgraded from a previous version prior to 2004, then the AFP protocol will need to be used. Prior to 2004, 4D followed the macintosh file convention, which was to have a resource fork and data fork all in one file. Thus, when upgrading a database from 2003 to 2004, the structure and data still use the previous macintosh file convention. This differs from a native 2004 database because there are four files rather than two.

Structure File (.4DB)
Structure Resource (.RSR)
Data file (.4DD)
Data Resource (.4DR)

If the SMB protocol is used to transfer the upgraded files, the file becomes unusable. This is because the resource fork information is lost during the transfer. However there is a workaround. The workaround is to archive the files. Mac OS X has a built in zip archive and extractor tool. Simply archive the file and transfer the file with SMB (AFP will work as well). After the file has been transferred extract the file.

In addition, the above information can also be applied to other files such as plug-ins .

Related Sources:

What can I do if I cannot select a file in 4D on a Mac?
http://www.4d.com/knowledgebase?CaseID=45072

Information on SMB protocol:
http://en.wikipedia.org/wiki/Server_Message_Block

Information on AFP protocol:
http://en.wikipedia.org/wiki/Apple_Filing_Protocol