Android OpenGL error in Unity 5 but not in Unity 4.6

I am calling native opengl functions to render to a framebuffer from unity. Specifically, I'm rendering a movie image to a framebuffer with a texture from unity attached. It all works in Unity 4.6 but when I moved the project to Unity 5, the program returns an invalid operation error after the glDrawElements function, and the image fails to render to the framebuffer.

Removing the glDrawElements function allows the program to run without errors, and I confirmed that changing the clear color does reflect the change in unity.

I suspect I am missing some step that by chance Unity 4 was doing, but not Unity 5, but I cannot seem to find it.

Can anyone help me?

Below is the code called every frame to draw to the framebuffer.

     public void DrawFrame() {
         
         synchronized(this) {
             if (updateSurface) {
                 updateSurface = false;
                 //Log.d(TAG, "Update texture");
             } else {
                 return; //no need to render texture
             }
         }
         
         checkGlError("preDrawFrame");
         
         //long drawStart = System.currentTimeMillis();
         mSurfaceTexture.updateTexImage(); //updates the texture mTexExtOES
         mSurfaceTexture.getTransformMatrix(mSTMatrix); 
         
         //bind fbo
         GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, mFBO);
         
         //GLES20.glDisable(GLES20.GL_DEPTH_TEST);
         GLES20.glDisable(GLES20.GL_CULL_FACE);
         //GLES20.glDisable(GLES20.GL_SCISSOR_TEST);
         //GLES20.glDepthMask(false);
         
         GLES20.glClearColor(0.0f, 1.0f, 0.0f, 1.0f);
         GLES20.glClearDepthf(1);
         GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);
         
         //shader
         GLES20.glUseProgram(mProgram);
         checkGlError("glUseProgram");
         
         
         //texture
         GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
         GLES20.glBindTexture(GL_TEXTURE_EXTERNAL_OES, mTexExtOES); //no need to bind, updateTexImage does that
         GLES20.glUniform1i(mExtSamplerHandle, 0); //make sure the sampler is bound to the right texture unit
         //GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureID);
         
         //position 
         GLES20.glEnableVertexAttribArray(maPositionHandle);
         checkGlError("glEnableVertexAttribArray maPositionHandle");
         GLES20.glVertexAttribPointer(maPositionHandle, 4, GLES20.GL_FLOAT, false, 0, mVertexBuffer);
         checkGlError("glVertexAttribPointer maPosition");
         
         //uv
         GLES20.glEnableVertexAttribArray(maTextureHandle);
         checkGlError("glEnableVertexAttribArray maTextureHandle");
         GLES20.glVertexAttribPointer(maTextureHandle, 2, GLES20.GL_FLOAT, false, 0, mTexCoordBuffer);
         checkGlError("glVertexAttribPointer maTextureHandle");
             
         //Apply the combined projection and camera view transformations
         GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0);
         GLES20.glUniformMatrix4fv(muSTMatrixHandle, 1, false, mSTMatrix, 0);
         
         GLES20.glViewport(0, 0, mTexWidth, mTexHeight); //render on the whole texture
         checkGlError("glViewport");
         
         GLES20.glDrawElements(GLES20.GL_TRIANGLE_STRIP, 4, GLES20.GL_UNSIGNED_SHORT, mIndexBuffer);
         checkGlError("glDrawElements");
         
         //reset //unnecessary since we call GL.Invalidate in unity anyway
         //GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
         //GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
         //GLES20.glActiveTexture(GLES20.GL_TEXTURE1);
         //GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
         //GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);
         //GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, 0);
         
         GLES20.glDisableVertexAttribArray(maPositionHandle);
         GLES20.glDisableVertexAttribArray(maTextureHandle);
         
         //restore bindings
         GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, 0);
     }