Using 'like' in ssrs expressions

SSRS does NOT use SQL syntax, but instead uses Visual Basic.

Use something like this:

=IIf(Fields!Notes.Value.IndexOf("deadline") >= 0,"Yellow","Transparent")

Or .Contains instead of .IndexOf

=IIf(Fields!Notes.Value.ToLowerInvariant().Contains("deadline"),"Yellow","Transparent")

It is like in access: not '%' but '*':

=Fields!Notes.Value Like "*deadline*"

"InStr" works for me:

=IIF(InStr(Fields!Notes.Value,"deadline")>0, "Yellow", "Transparent") 

Remember that the compare value is case-sentive, so maybe use UCASE around:

=IIF(InStr(UCASE(Fields!Notes.Value),"DEADLINE"))>0, "Yellow", "Transparent")