The error message says that the same column cannot be selected both with and without aggregation. One solution is to move the count function to another column:

=query(A:B, "select toDate(A), count(B), sum(B) group by toDate(A)")

Another solution, which is also applicable when there is no column B, is to duplicate column A before querying: {A:A, A:B} is the array with three columns in which the column A appears twice. One can refer to these columns as Col1, Col2, Col3 in the query string. The following formula returns the desired table:

=query({A:A, A:B}, "select toDate(Col1), count(Col2), sum(Col3) where Col1 is not null group by toDate(Col1) label toDate(Col1) 'date'")

For readability, the same query string with linebreaks:

select toDate(Col1), count(Col2), sum(Col3) 
where Col1 is not null 
group by toDate(Col1) 
label toDate(Col1) 'date'

The error message is due to a missing closing parenthesis before the first AND.

Once solving this, you will get as result the following

            sum     sum 
10/12/2016  296.1   2.5

To avoid the headers, before the last " add

 label sum(Col8) '', sum(Col9) ''

the final formula is

=QUERY(ARRAYFORMULA(IMPORTRANGE(
"https://docs.google.com/spreadsheets/d/1Wyewpz0j_IiKK8ESOapX5L4AedjvHccLZOOKS2tZGUA/",
"UsuallyAnotherSpreadsheetFile!B2:K")),"Select Col4, sum(Col8), sum(Col9) where  
(Col4=date '"&TEXT(A14,"yyyy-mm-dd")&"') AND (Col3='" & $F$1 & "')  AND 
(Col1 = '" & ClientInfo!$H$1 & "') group by Col4 label sum(Col8) '', sum(Col9) ''")