[BetterRed]

@Alaa - don't worry about reporting the 'bug', I took it up with chaley in this thread ==>> Problem with template functions and library maintenance

@chaley - I did some tests on an fresh empty library and I could not reproduce the TEMPLATE ERROR... I saw previously. Happy to write that down to me not doing a restart when I should have done, or using a much abused library

But I did find an anomaly that could be related. Here is a blow-by-blow script of what I did (twice - i.e. it's repeatable)

create two custom columns - 
	#first_location/First Location, 
             Long text . . . 
             header on the side,
             HTML
	#second_location/Second Location, 
             Long text . . . 
             header on the side, 
             HTML
	Apply and Restart
create two virtual libraries
	Has First Loc, #first_location:true
	Has Second Loc, #second_location:true 
create two custom columns (to test if tags-like was relevant - it seems not) 
	#virtlibs_like_tags/Virtual Lib Like Tags, 
		column built from other columns, behaves like Tags, 
		Sort/search column by Text, 
		Show in tags browser: unchecked, 
		Show as HTML in book details unchecked 
	#virtlibs_not_tags/Virtual Lib Not Tags, 
		column built from other columns, 
		Sort/search column by Text, 
		Show in tags browser: unchecked, 
		Show as HTML in book details unchecked 
		Apply and Restart

Put some data in First Location and Second Location- everything OK, the two VL columns were updated dynamically and no TEMPLATE Error... msgs.

Added a Third Location, same as First and Second, Put some HTML values into Third Location.

Added another VL - Has Third Loc, books with a Third Location appeared in the VL. However the Virtual Libs columns didn't update to show the Has Third Loc VL . . . until I did a restart

But once I'd done a restart. the Virt Lib columns updated dynamically.

Looks to me if as the template {:'virtual_libraries()'} is only evaluated (goes looking for VLs) when a library is opened. Ideally I guess it should refresh if a VL is added, edited, or removed, or less ideally any VL add/edit/remove should ask for a restart a'la custom columns...

Hope this makes sense

BR