Help needed with Registar please.

[oldannie]

I usually stack in DSS and process in photoshop but recently bought Registar and used it for the first time yesterday as I have some Ha, LRGB subs (taken over several nights) of M101 which I would like to align and combine.  All the LRGB subs are 300sec, 1x1 binning and imaged through Baader 7nm filters. The Ha subs are 600secs, binning 1x1 using Chroma 3nm filter.  Am happy with the process of aligning and cropping/padding each channel in Registar but am confused about combining each channel and then aligning the Ha and Luminance with the RGB  file.  If I use DSS to stack each channel a 32 bit tif file is produced which Registar will not open.  I get the following message ' Please ensure the file has not been compressed using a proprietary compression scheme' ? 

Thanks

Annie