You could try to set all the tracks to Don't Follow and then change the BPM to 100. I think you will find everything (including your overdubs) will stay the same except for the BPM which is what you are after.

If you have dragged material or audio starts at bar 1 then everything should line up OK. If not though once you have reset the BPM to 100 then you might have to select everything and lineup the start (of everything) to a bar e.g. bar 1 or later.

Thanks for this

Hi...well that worked a treat regarding timing, however ...on the new 100BPM version the fader levels are all different to before?....why would that be?

Well not sure on that. Is there automation involved. Chances are the automation might be in a different place in terms of timing now perhaps not sure. At least you have got everything lined up better now. You should also enter the tempo values into the audio files too from the inspector. Then you can time stretch the whole session if you need to take it up or slow it down a tad. Switch the tracks from Don't Follow to Timestretch instead.

Its easy to forget about tempo settings when bringing in new sessions so I certainly feel the pain there and have been guilty of it myself. But at least you won't do it again!

When you do bring in sessions as well from other DAW's and the tempo say might be 100 BPM a good thing to do is to line up bar 1 in Studio One (or bar 3 actually) to be right on the very first transient and then check the timing right at the end of the song as well. It might be very slightly out at the end and you may have to tweak the Studio One tempo to 99.8 or 100.2 etc in order to get the very end in sync as well. (assuming it was all done to a click) I have encountered very slight differences between some DAW's like this. No biggie as it is easy to correct. Mostly though due to digital being so accurate it will be spot on.