sql - Cannot update multiple records in table which has a trigger configured

Question

I run the following query:

update XFolder
set isdeleted = 1
where XFolder.XFolderID in (select FundRaiseXFolder.XFolderID from FundRaiseXFolder where FundRaiseID = 6233)

I am getting following error:

Msg 512, Level 16, State 1, Procedure Fippex_UpdateXFolderCacheTableForPrivatePublic, Line 20
Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

This used to work fine until I added trigger on table xfolder.