Heyyo,
I'm having the same problem. My latest waypoints were done in EPB v5.2... Maybe the last couple of hl1 engine updates killed epb's compatiblity, cause I know last Source Engine update for the cl_interp_ratio killed 64bit compatibility for HL2 and HL2 Lost Coast.
Oh, I also tested EPB v5.3 with CZero, and it doesn't finish loading either.