XML not well formed (invalid token) - xamarin

Question

When I am trying to build my app using xamarin for android, an error pops up saying
Error parsing XML: not well-formed (invalid token) in line 17
I cannot seem to find where the bad structure is though. As it seem, it has something to do with the way I try to include buttons in the grid layout. I am sure it is something stupid but I just cannot find it. I included my code below:
New error:
Error parsing XML: unbound prefix in line 17
<?xml version="1.0" encoding="utf-8"?>
<GridLayout>
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:minWidth="25px"
android:minHeight="25px"
android:layout_width="match_parent"
android:layout_height="fill_parent"
android:id="#+id/gridLayout1"
android:paddingLeft="40"
android:alignmentMode="alignMargins"
android:columnCount="3"
android:rowCount="20"
<Button
android:text="Button"
android:id="#+id/button1"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button2"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button3"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button4"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button5"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button6"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button7"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button8"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button9"
android:height="100"
android:width="100" />
<Button
android:text="Button"
android:id="#+id/button10"
android:height="100"
android:width="100" />
</GridLayout>

Answer 1

If you count the line 17 that it points out to, you reach this line
android:height="100"
Notice the "unbound prefix" or how there is no unit (dp/sp) against that value.
Please fix that and all the other length measurements to contain a unit of measurement, so that the prefix is bound:
android:height="100dp"