INVALID_ENUM warnings

Hi,

I am a html programmer having my first dig into webgl. I was running some webgl demos in google-chrome and logged the gl commands by using apitrace. My system information is:
OS ubuntu 11.10
GL version 2.1
GL_VENDOR Tungsten Graphics, Inc
GL_RENDERER Mesa DRI Intel® Sandybridge Mobile x86/MMX/SSE2
GL_VERSION 2.1 Mesa 7.11
2d GraphicsBackend: SKia

I observed that there are plenty of warnings.Various functions produce a glGetError value of INVALID_ENUM.

Some of them being:
1)glGenerateMipmapEXT when target is GL_TEXTURE_2D or GL_TEXTURE_CUBE_MAP. I do have the GL_EXT_framebuffer_object extension.
2)glViewPort(x=0,y=0,width=1042,height=643). This is called after eglMakeCurrent.
3)glDisable(cap=GL_STENCIL_TEST) to name a few.
any tips on how to find the root causes for these warnings , Can these be ignored or does it mean there are issues which effect the overall stability and performance of webgl

Thanks in advance,
Madhav