Just tested your last build: using wimlib-1.7.0-BETA-windows-x86_64-bin and your x64 .exe in same file (now at the root of my Win7SP1x64 partition), selected same XP partition to make the image from it, but when I clicked capture the Info window opened and checked how many files and folders to be copied, when finished it stops there.
Clicking OK I go back to capture window again, clicking run: a Command prompt opens and it said there is an error Boot\BCD : Can't open file <status=0xc0000043>: Resource busy ERROR: Exiting with error code 47: Failed to open a file Errorlevel =47.
Well this may be caused because I have a dual booting XP/Win7:
First primary partition: XP and Win7 boot files NTFS Active
Second primary partition: Win7
Third primary partition: documents
Second HDD: Single NTFS primary partition
As I was runing your tool from Win7, trying to make an image of XP, the boot files corresponding to win7 where unavailable.
I then rebooted to MistyPE-7x64.ISO from my HDD using grub4dos and tryed again (running your tool from Win7 partition on HDD), this time when clicked Capture the Info window opened and started capturing, capture finished OK but I had selected Recovery compression, it should be .esd not .wim, and my final image was .wim; I think you need to fix that.