ok, managed to get this working by doing a replace on the parameter to replace ' with ''

That's the thing, I get the error even without any code written. it fails as soon as I add in the web reference (which it connects to fine).
the web...

the whole string is as follows:
set @querytext = replace('BEGIN:VCALENDAR~~VERSION:2.0~~METHOD: PUBLISH~~' + stuff((SELECT SelectString2 + '' FROM triage.dbo.vw_ExportLists_ics_2 FOR XML PATH('')),1,0,'') +  'END:VCALENDAR','~~', char(13));
this prints in SSMS as:
BEGIN:VCALENDAR