Thanks for the reply Arnold.
The formula I am using for comment read is
EPMCommentFullContext(,$XX,$YY,$ZZ,etc..,EPMMemberID(x26),$Y1)
I am using epmmemberid to reference it within the EPMcommentfullcontext(). When the formula reaches the local member, it cannot find the relevant olap member so it is showing this error.
With iserror(EPMCommentFullContext(,$XX,$YY,$ZZ,etc..,EPMMemberID(x26),$Y1)) it will still show it as false so we are back to square one.
Regards,
David