Maybe this is more hardware related than SOFTWARE but will try here first...

USING Win.XP Home SP.2 and Nero 5.5 I burned a folder and six files to a cdrw.  At a later time I added a further six files in one session.  The first seven items are accessible using XP but the others are not visible when the cdrw is opened or when Dir is run at the command prompt using the same cd writer.  Also tried another two pc's and a laptop all RUNNING XP Home with the same result.  

However, using a pc running Win.98se all files are accessible.  Just to CHECK it out I swapped the original cd writer into the pc running Win.98se and was able to access all files.

Visually the cdrw appears to have an area where data has been burned then a "gap" then a further burned area.

As you'll appreciate this is not a problem as all data can be or has been recovered using Win.98se, I'm just curious as to what circumstance(s) might have caused XP to falter.  No other multi-session cdrw's burned both before and after this one have caused any problems.

Thanks.

Edit: To add to my confusion I burned a copy of the cdrw and [highlight]all[/highlight] files were burned and accessible on the copy....Chances are the CD was never "finalised in the BURN process...the fact you were able to later add files illustrates this.
DLoad and install ISOBuster which can read a non finalised burn then move your files back to the HDD and re-burn the project the way you want to and remember to finalise the CD