attempt to call a Instance value when sending instance to function?

I have been experiencing this issue in my code and haven't figured out why it is returning this error: attempt to call a Instance value when I send an instance to a function

The line of code and some of the code around it:

sitemr = script.Parent.Hotbar[tostring(b)]
            if sitem.amount > 1 then    
                sitemr.ImageLabel.TextLabel.Text = sitem.amount
            else
                sitemr.ImageLabel.TextLabel.Text = ""

            end
            if sitem.amount > 0 then
                if minecraftitems[sitem.itemtype] then
                    sitemr.ImageLabel.Image = minecraftitems[sitem.itemtype]
                end
                if not minecraftitems[sitem.itemtype]and blocks[sitem.itemtype]then
                    if not sitemr.ViewportFrame.Block:FindFirstChildOfClass("Texture") then 
                        tex(sitemr.ViewportFrame.Block,sitem.itemtype,false,false,false,false,false,false)
                    end
                end
            else
                sitemr.ImageLabel.Image = ""
                sitemr.ViewportFrame.Block.Transparency = 1
                sitemr.ViewportFrame.Block:ClearAllChildren()
            end

function texturize(part,blocktype,left,right,front,back,topp,bottom)
    if blocks[blocktype].onetexture == true then 
        if not front then
            top=tex:Clone()
            top.Name = "TexFront"
            top.Parent = part
            top.Texture = blocks[blocktype].tex
            top.Face = "Front"
        end
        if not back then
            top=tex:Clone()
            top.Name = "TexBack"
            top.Parent = part
            top.Texture = blocks[blocktype].tex
            top.Face = "Back"
        end
        if not left then
            top=tex:Clone()
            top.Name = "TexLeft"
            top.Parent = part
            top.Texture = blocks[blocktype].tex
            top.Face = "Left"
        end
        if not right then
            top=tex:Clone()
        top.Name = "TexRight"
        top.Parent = part
        top.Texture = blocks[blocktype].tex
            top.Face = "Right"
        end
        if not topp then
            top=tex:Clone()
        top.Name = "TexTop"
        top.Parent = part
        top.Texture = blocks[blocktype].tex
            top.Face = "Top"
        end
        if not bottom then
            top=tex:Clone()
        top.Name = "TexBottom"
        top.Parent = part
        top.Texture = blocks[blocktype].tex
            top.Face = "Bottom"
        end
    else
        if not front then
            top=tex:Clone()
            top.Name = "TexFront"
            top.Parent = part
            top.Texture = blocks[blocktype].texfront
            top.Face = "Front"
        end
        if not back then
            top=tex:Clone()
            top.Name = "TexBack"
            top.Parent = part
            top.Texture = blocks[blocktype].texback
            top.Face = "Back"
        end
        if not left then
            top=tex:Clone()
            top.Name = "TexLeft"
            top.Parent = part
            top.Texture = blocks[blocktype].texleft
            top.Face = "Left"
        end
        if not right then
            top=tex:Clone()
            top.Name = "TexRight"
            top.Parent = part
            top.Texture = blocks[blocktype].texright
            top.Face = "Right"
        end
        if not topp then
            top=tex:Clone()
            top.Name = "TexTop"
            top.Parent = part
            top.Texture = blocks[blocktype].textop
            top.Face = "Top"
        end
        if not bottom then
            top=tex:Clone()
            top.Name = "TexBottom"
            top.Parent = part
            top.Texture = blocks[blocktype].texbottom
            top.Face = "Bottom"
        end
    end
end

Thanks in advance!