What image type are you trying to capture to? What version of LDMS are you using? Is your PXE Rep also a Preferred Server, and if so are you trying to store the captured image file(s) there or on the core server?
The relevant logs should be located on the client at X:\ldprovision. You can also check the logs at \\yourcoreserver\ldmain\log\Provisioning.
You checked the permissions to the share on the PXE rep with NET USE, but does the exact folder you're trying to capture to exist? For example, I have an images share on my PXE Reps\Preferred Servers located at C:\Images, but I capture to the C:\Images\Capture subfolder. If the capture subfolder doesn't exist you'll receive an error.