Does your class have a relationship property to another class?
In that case you might want to consider to use: "CompileAfter"  or "DependsOn" keywords (those might help the compiler to have a correct order when compiling). 

maybe there are dependencies for that class? (e.g. class depends on another class(es) that need to be compiled before). try to add "r" (recursive) flag, so your flags will look like: "ckr"

You have other 2 options:
1. With SQL against the %SYS.Task class/table (delete from %SYS.Task where id=taskID)
2. Set sc = ##class(%SYS.Task).%DeleteId(taskID)