I am trying to model an unbaffled stirred tank using MRF and the RSM turbulence model. However, after 17 iterations, I get a message "turbulent viscosity limited to viscosity ratio of 1.0e+05 in 1 cells. The number of cells affected then rises with each iteration until iteration 23 when I get the message "turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 2439 cells. Error: Floating point error: overflow".

From other postings on this site I know that this is an issue which many people face. Could someone please give me some advice?

you can improve the ratio in the solve--control--limits,maybe that can help.