Sometimes FLV files downloaded from youtube or flash page via stream recorders such as Real Player are corrupted. Hence, not able to seek, especially in smartphone (ie. Android, etc.).
In my phone, such videos had to be played from beginning to the end continuously. I cannot skip to the middle track.
The best fix thus far is a freeware called Avidemux.
Save flv files in mp4 format and videos will be seek friendly.