When a topic contains an xref that uses a topic ID instead of a filename in the href, dita2Confluence gives an error. But the topic that the (rather cryptic) error is reported against is the one subsequent to the one with the problematic xref in the ditamap.
In the attached project, topic1.xml contains an xref to "topic2_id" (the ID of the topic in topic2.xml). When you run this with dita2Confluence, the following error is reported:
[Dita2Confluence] ERROR - Problem processing xml: C:/temp/ditatest/topic2.xml
[Dita2Confluence] java.io.FileNotFoundException: C:\Tools\dita2confluence1.2.2\C:\Tools\dita2conflluence1.2.2\C:\Tools\dita2confluence1.2.2\files\concept.dtd (The filename, directory name, or volume label syntax is incorrect)
Note that it doesn't matter what follows topic1.xml in the ditamap; you can change the order of the files, and the one after topic1 is what gets the error.
Using a (bare) topic ID in an xref is not permitted by the DITA 1.1 spec (http://ditainfocenter.com/eclipsehelp/index.jsp?topic=/org.ditausers.infomanager.LangSpec1.1/langref/xref.html), but the error should be reported against the file that contains the problem. Even better, it should describe what's wrong.
CME dita project for this issue