Now it's broken again, without making any changes. I am seeing this error desribed here while trying to map to the express share (1223 invalid password):
https://kb.altiris.com/article.asp?article=33131&p=1
I have re-entered the credentials for WinPE and rebuilt the PXE image numerous times with no luck. Checked the NTFS permissions for the account. I checked the DS and it is using NTLM authentication. Everything 10th time it will actually work. Why it isn't working the rest of the time I do not understand.