This error message indicates that GAMS has a problem to rewrite some temp parameter files, which are written/read and rewritten several time. GAMS will create some unique directories like 225a in the directory you started the GAMS run. If this drive is a network drive, i.e hosted on another machine it may be possible that the time is not well enough synchronized between the machine that is executing GAMS and the machine that is hosting the project directory.