What does the "*" in haplogroup I2A1* mean?
From the 23andMe website:


  Sometimes there are a few lineages that don't fit into any subgroup of a haplogroup. Since there isn't a mutation that links these lineages, they don't get their own subgroup. Instead, these lineages are given the main haplogroup label plus a star (*) to indicate that they are part of the main haplogroup but don't fit into any of the known subgroups


So there are defined subgroups for I2A1 (I2A1A and I2A1B) for which more information is available, but you dont fit into any of them. 

What "doesn't move down stream" means, I have no idea.