Link to additional reference in TOC

Link to additional reference in TOC

In SHFB, I have some standard topics and some namespaces imported from
some references. I also have a custom HTML page (called ZenDesk.html) that
I have added as content in a new "CRM Plugins" folder.
I am trying to link to this page from the "Welcome" topic page using
<link xlink:href="CRM Plugins/ZenDesk.html">Zendesk</link> plugin
I have tried
/CRM Plugins/ZenDesk.html
./CRM Plugins/ZenDesk.html
./CRM%20Plugins/ZenDesk.html
/html/CRM%20Plugins/ZenDesk.html
/html/CRM Plugins/ZenDesk.html
too but without success. The page URL property from the CHM file shows
mk:@MSITStore:D:\BridgeServerDocumentation.chm::/CRM%20Plugins/ZenDesk.html
The build log file shows this error:
Warn: ResolveConceptualLinksComponent:
[cc965c65-04b5-4e2c-8525-559ed65e4717] Invalid
conceptual link target './crm%20plugins/zendesk.html'.
Finally, while the CHM compiles, I can see a "CRM Plugins" folder in the
"Output" folder.
What am I doing wrong?