"Like" doesn't do anything when used with a number; it is only useful with text.
You would have to concatenate the value, right now you are saying shoul me records where "gymnastID" is like Me.gymnastID.
The correct syntax would be
Forms!frmGymnastFilter.Filter = "Forms!frmGymnastFilter.gymnastID = " & Me.gymnastID
It is easier to use the filter argument or the where argument of the "DoCmd.OpenForm" command.
The syntax is
DoCmd.OpenForm(FormName, View, FilterName, WhereCondition, DataMode, WindowMode, OpenArgs)
Your procedure could be
Code:
Private Sub cmdOpenGym_Click()
DoCmd.OpenForm "frmGymnastFilter", , "gymnastID = " & Me.gymnastID
End Sub
This is provided "Me.gymnastID" is a number....