Error with Nero AAC encoder in XVID4PSP - "Could not open AAC encoder&

[TheViking]

I'm trying to convert an avi file to PSP format. I use XVID4PSP as many times in the past with great success. However, with quite a large bunch of files now, I get this error:
"Could not open AAC encoder"

I find this very strange and cannot see any reason why these files would give an error (as opposed to the files that covert fine).

GSpot gives me this:
Files with no error:

AUDIO_BITRATE                  384
AUDIO_BITRATE_TYPE             CBR
AUDIO_CHANNEL_COUNT            6
AUDIO_CODEC                    0x2000 (Dolby AC3) AC3
AUDIO_CODEC_STATUS             Codec(s) are Installed
AUDIO_MPEG_STREAM_ID           
AUDIO_MPEG_SUBSTREAM_ID        
AUDIO_SAMPLE_RATE              48000

Files with error:

AUDIO_BITRATE                  192
AUDIO_BITRATE_TYPE             CBR
AUDIO_CHANNEL_COUNT            2
AUDIO_CODEC                    0x2000 (Dolby AC3) AC3
AUDIO_CODEC_STATUS             Codec(s) are Installed
AUDIO_MPEG_STREAM_ID           
AUDIO_MPEG_SUBSTREAM_ID        
AUDIO_SAMPLE_RATE              48000

I cannot see why XVID4PSP (latest version) or Nero AAC encoder is doing this.

[usta]

Try installing AC3Filter.

[TheViking]

False alarm.
I tried a fresh install within a virtual machine. Success.
I also installed AC3Filter on my regular box. Success.

Must be something broken with my original install...

Thanks for your help.