RH9 on Win7 - won't change styles

When I am working on a document imported from Word, RH9 is not allowing me to change the styles from the MS_Word styles to my RoboHelp master .css.

When I highlight a line to be changed, I get the message "Reapply style" - I click on Reapply and then get a message which says:A Style name cannot contain spaces or begin with a digit ...    However, I'm not using a style name with spaces or beginning with a digit.  My style name is just the standard "Normal".  Then RH will not allow the style to change from whatever the "MS_" style is.

The original word document was heavily edited with track changes - could that be part of the problem?

I have never had this message before working on this particular document.

Some sections of the document have converted without a problem!!  Which adds to my frustration!