I am trying to import a .xml file, but the following message keeps coming up.
"Cannot open the file "filename.xml". Adibe InDesign may not support the file format, a plug-in that supports the file format may be missing, or the file may be open in another application"
I can say for sure that the file is not open in another application.
What version of InDesign?
How are you importing the XML file?
What are the first few lines of the XML file?
Sounds like you are trying to "Open" the XML file in ID rather than creating a document and then IMPORTing the XML.