I've used Solomon Messing's tutorial (see link below) on how to export data from CAT to R with great success. However, when only 3/4 coders have completed coding the dataset I run into problems. Even if I delete those documents that have not been coded by all coders it seems that R is unable to parse the XML file. My guess is that the XML file from CAT is set up for the initial number of documents and coders, so that when documents and coders are removed the R script is no longer compatible. Is there a way to modify the XML file or even remove coding by certain coders? The console output looks like this: 
(I have no problems with odd characters when coding is complete by all coders.)

> 
> doc <- xmlInternalTreeParse(doc, asText=T)
> 
> 
> 

xmlParseCharRef: invalid xmlChar value 0

xmlParseCharRef: invalid xmlChar value 0

xmlParseCharRef: invalid xmlChar value 0

xmlParseCharRef: invalid xmlChar value 0

Error: 1: xmlParseCharRef: invalid xmlChar value 0

2: xmlParseCharRef: invalid xmlChar value 0

3: xmlParseCharRef: invalid xmlChar value 0

4: xmlParseCharRef: invalid xmlChar value 0

5: xmlParseCharRef: invalid xmlChar value 0

6: xmlParseCharRef: invalid xmlChar value 0

<http://solomonmessing.wordpress.com/2013/02/04/cat-r-for-content-analysislabels-for-text-mining/>