The rheological properties of a PEO-PPO-PEO copolymer in aqueous solutions have been studied in the gel-like zone of its phase diagram. This polymer is the Pluronic (R) P105 (EO37-PO56-EO37). If the temperature or the concentration is high enough, the polymer forms micelles and the micelles can condense into crystalline phases. This linear copolymer has a complex behavior since the micelles can form different structures: hexagonal, body centered, and lamellar. But, whatever the structure, the condensed phases exhibit the rheological characteristics of viscoelastic fluids. However, these properties are strongly dependent on the value of the stress applied during the spectromechanical experiment. Stress-time relationships are also observed in steady experiments. Indeed, the solutions behave as yield stress fluids and the apparent yield stress depends on the time during which the stress is applied. A generalization of the Eyring's model allows a good description of this atypical behavior.