  We report that single crystals of (Ba,K)Fe2As2 with Tc = 32 K have a pinning
potential, U0, as high as 10^4 K, with U0 showing very little field
depend-ence. In addition, the (Ba,K)Fe2As2 single crystals become isotropic at
low temperatures and high magnetic fields, resulting in a very rigid vortex
lattice, even in fields very close to Hc2. The rigid vortices in the two
dimensional (Ba,K)Fe2As2 distinguish this compound from 2D high Tc cuprate
superconductors with 2D vortices, and make it being capable of cearrying very
high critical current.Flux jumping due to high Jc was also observed in large
samples at low temperatures.
