Selenium modal Xpath can't Locate - html

Question

I need to select this input
`(name="BtnOK" value="TAMAM" class="BoxButtonOK")`
with xpath after this modal popup. I can't use .FindByClass because there are same classes in the main page, but I need open which in (id="__LIGHTBOX__") modal, and when I use xpath sometimes it gives me error "cant locate element" and oddly sometimes it works.
Here is my code for xpath (and yes I already tried wait.until and no progress):
//div[contains(#id, 'LIGHTBOX')]//input[#name='BtnNext' and contains(#class, 'NavigationButtonNextLightBox')]
And here is modal:
<div id="__LIGHTBOX__" style="overflow: visible; padding: 0px; width: auto; min-height: 143px; max-height: none; height: auto;" class="ui-dialog-content ui-widget-content" >
<div class="__BOX__">
<input name="BtnClose" class="BoxButtonClose" type="button">
<div>
<img src="/Content/themes/base/images/popup-bg-top.png">
</div>
<div class="popupCapsule clearFix">
<div class="banner clearFix">
<h1 class="pageTitle">Fatura Ödeme</h1>
</div>
<div class="noteCapsulePopupContainer">
<div>
<img src="/Content/themes/base/images/note-capsule-top-success.png">
</div>
<div class="noteCapsulePopup">
<table>
<tbody>
<tr>
<td class="waitingTd"></td>
<td>
<p id="TransactionFlowNote">
<span>
<span class="important">10177202-1 (Beşyüzevler Şube)</span> adlı hesabımdan <span class="important">27,50 TL</span> tutarındaki <span class="important">5387373484</span> abone numarasına ait <span class="important">TURKCELL</span> faturası kurumuna iletildi, borcunuz kısa süre içerisinde tahsil edilecektir.
</span>
</p>
</td>
</tr>
</tbody>
</table>
</div>
<div>
<img src="/Content/themes/base/images/note-capsule-sub.png">
</div>
</div>
<table class="popupButtonArea">
<tbody>
<tr>
<td class="left"></td>
<td class="right">
<input name="BtnSlip" value="DEKONT" class="popupOpenLink" style="margin-right: 5px;" href="/Slip/Index/201504220001012380000019284/" type="button"><input name="BtnPeopleAndPlaces" value="İŞLEMİ KAYDET" class="popupOpenLink ButtonWide2" style="margin-right: 5px;" href="/PeopleAndPlaces/SaveTransaction/201504220001012380000019284/1238/False" type="button">
<input name="BtnOK" value="TAMAM" class="BoxButtonOK" type="button">
</td>
</tr>
</tbody>
</table>
</div>
<div>
<img src="/Content/themes/base/images/popup-bg-sub.png">
</div>
</div>

Answer 1

Select by name:
WebElement btnNext = driver().findElement(By.name("BtnOK"));

Answer 2

Selected by Xpath
WebElement btnNext = driver().findElement(By.Xpath("//input[#name='BtnOK']"));