When I upgraded from 15.1.2 to 15.1.3 the CalendarExtender stopped working and it appears the MaskedEditExtender is causing it. Tested by disabling the MaskedEditExtender and the CalendarExtender works again. I rolled back to 15.1.2 until resolved.
While on the subject: If the CalendarExtender had a couple of basic parameters like InputMask, InvalidValueMessage I could eliminate both the MaskedEditExtender and the MaskedEditValidator.
<asp:TextBox ID="txtInvoiceDate" runat="server" Text="" Width="150px" MaxLength="10" />
<ajax:MaskedEditExtender ID="MaskedEditExtender1" runat="server" TargetControlID="txtInvoiceDate" MaskType="Date" Mask="99/99/9999" UserDateFormat="MonthDayYear" PromptCharacter="_" Enabled="true" />
<ajax:MaskedEditValidator ID="MaskedEditValidator1" runat="server" ControlToValidate="txtInvoiceDate" ControlExtender="MaskedEditExtender1" InvalidValueMessage="* Invalid Date" IsValidEmpty="False" ForeColor="Red" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" Text="* Required" ControlToValidate="txtInvoiceDate" ForeColor="Red" Display="Dynamic" SetFocusOnError="true" />
<ajax:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="txtInvoiceDate" Format="MM/dd/yyyy" Enabled="True" ValidateRequestMode="Enabled" />
Comments: Set you message requesting screen share and conference call to better demonstrate the issue.
While on the subject: If the CalendarExtender had a couple of basic parameters like InputMask, InvalidValueMessage I could eliminate both the MaskedEditExtender and the MaskedEditValidator.
<asp:TextBox ID="txtInvoiceDate" runat="server" Text="" Width="150px" MaxLength="10" />
<ajax:MaskedEditExtender ID="MaskedEditExtender1" runat="server" TargetControlID="txtInvoiceDate" MaskType="Date" Mask="99/99/9999" UserDateFormat="MonthDayYear" PromptCharacter="_" Enabled="true" />
<ajax:MaskedEditValidator ID="MaskedEditValidator1" runat="server" ControlToValidate="txtInvoiceDate" ControlExtender="MaskedEditExtender1" InvalidValueMessage="* Invalid Date" IsValidEmpty="False" ForeColor="Red" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" Text="* Required" ControlToValidate="txtInvoiceDate" ForeColor="Red" Display="Dynamic" SetFocusOnError="true" />
<ajax:CalendarExtender ID="CalendarExtender1" runat="server" TargetControlID="txtInvoiceDate" Format="MM/dd/yyyy" Enabled="True" ValidateRequestMode="Enabled" />
Comments: Set you message requesting screen share and conference call to better demonstrate the issue.