BadParameter error from VENC at target bitrates > 60 Mbps

We're using version 5.04.00.11 of the EZSDK on a DM8148-EVM to encode video to H.264.  At target bitrates up to about 60 Mbps, it works fine.  However, at 70 Mbps and above, we get a OMX_ErrorBadParameter error from VENC.  I am setting the bitrate in bits per second (e.g., 70000000) via these calls:

 tPortDef.nPortIndex = OMX_VIDENC_OUTPUT_PORT;

rc = OMX_GetParameter (_comp_handle, OMX_IndexParamPortDefinition, &tPortDef);

tPortDef.format.video.nBitrate = bitrate;

OMX_SetParameter (_comp_handle, OMX_IndexParamPortDefinition, &tPortDef);

and

    tVidEncBitRate.nPortIndex = OMX_DirOutput;

    rc = OMX_GetParameter (_comp_handle, OMX_IndexParamVideoBitrate, &tVidEncBitRate);

    tVidEncBitRate.nTargetBitrate = bitrate;

    rc = OMX_SetParameter (_comp_handle, OMX_IndexParamVideoBitrate, &tVidEncBitRate);

All of these calls succeed, but then VENC reports the bad parameter error.

Is there a maximum target bitrate that I'm exceeding?

Thanks!

- Dave Beal