On some tracks I play from my SD card on the Bolero, the track time progress bar is present. But on other tracks there is nothing and it says "VBR" on the right hand side.

Anyone know why?

VBR in MP3 terms stands for "Variable Bit Rate". It may be that the software on the Bolero can't work out how long a Variable Bit Rate track is because it's not predictable. If you have an MP3 in a constant bit rate then you can work it out:

(Filesize in Megabytes * 1024 * 8) / number of kilobits-per-second = number of seconds

But for VBR tracks, quiet/simple parts of the track will compress much better (i.e. need fewer kilobits of data per second to accurately represent the sound) and loud, complex parts of the track will need more kilobits. The player can't tell until it gets to a particular point in the track how many kbps it's actually using, so it's impossible to time it correctly without pre-reading the whole track (which a media player on your computer would do, but maybe the Bolero unit doesn't).

It may well be fixable by filling out the metadata on the MP3s with the correct length, if you're that bothered

Thanks GAC - most of my tracks (which are either iTunes or ripped from CD) do show the track time, it is just the odd few which I have acquired show the VBR.

Thanks for comprehensive reply!