When changing the calculation type in Classical mode from e.g. Plastic to Plastic Drained or to Consolidation, and vice versa, and you have set the groundwater flow conditions to be transient, the groundwater flow analysis is reset to a steady state analysis in the background. If you have defined transient groundwater flow conditions, please make sure to check these prior to your calculation.
If you have defined transient groundwater flow conditions, please make sure to check these prior to your calculation, and set the correct type of groundwater flow.
This has been fixed since PLAXIS 2D 2011.00