Cannot get inner content error - vb.net

Question

I'm in the process of migrating a website from one of my clients staging servers to a hosted server for one of their clients.
Everything else is working fine except the media gallery section of the website. When trying to open a gallery page I'm getting the error:
Cannot get inner content of ulGallerySlides because the contents are not literal.
I'm more of a techie than a programmer so I'm a bit stumped as to what is causing this and how to fix it. It works perfectly on the staging server.
The staging server is an IIS 7 server which I have full control over and the new server is hosted at an ISP on IIS 8 and I have very little control of it (just through WebSitePanel)
The code behind it is:
Public Sub BuildGalleryView()
Dim objDA As New clsDataAccess
Dim dtResults As New DataTable
Dim iCounter As Integer = 0
Dim intGalleryID As Integer = CInt(Request.QueryString("g"))
Dim strGalleryTitle As String = ""
Dim strGalleryDescription As String = "Test Gallery Description"
Dim strMediaTitle As String = "Test Media Title"
Dim strMediaDescription As String = "Test Media Description"
Dim strMediaURL As String = "./assets/images/placeholder.jpg"
dtResults = objDA.ODSGetGalleryMedia(intGalleryID).Tables(0)
'Set the gallery info first
strGalleryTitle = dtResults(0)("Gallery_Title").ToString
strGalleryDescription = dtResults(0)("Gallery_Description").ToString
lblGalleryTitle.InnerText = strGalleryTitle.ToString
lblGalleryDescription.InnerText = strGalleryDescription.ToString
lblGalleryMainTitle.InnerText = strGalleryTitle.ToString
If Not dtResults Is Nothing Then
'Loop through all the images and build the slider"
For i As Integer = 1 To dtResults.Rows.Count
strMediaTitle = dtResults(iCounter)("Media_Title").ToString
strMediaDescription = dtResults(iCounter)("Media_Description").ToString
strMediaURL = "./assets/" & dtResults(iCounter)("Media_URL").ToString
ulGallerySlides.InnerHtml = ulGallerySlides.InnerHtml & _
"<li>" & _
"<img src='" & strMediaURL & "' align='Slider'/>" & _
"<div class='flex-caption'>" & _
"<h2>" & strMediaTitle & "</h2>" & _
"<p>" & strMediaDescription & "</p>" & _
"</div>" & _
"</li>"
iCounter = iCounter + 1
Next
End If
End Sub
What do I need to change to fix this?