It seems that Mike Gascoyne and Toyota are not happy with each other, Gascoyne has been suspended due to "fundamental difference of opinion with regard to the technical operations". What that probably means is that Toyota is not happy with the strict an open way that Gascoyne runs his team.
Toyota where rumored to be paying Gascoyne the highest wage in the F1 game for his particular services, due to the fact he transformed the Renault team in his time there.
It is said that Toyota will probably assign Pascal Vasselon the job. Toyota picked him up from Michelin at the end of last year.
Not bing privy to the conversations that have gone on between Toyota and Gascoyne I cannot comment on why the break-up has actually happened; however I think if Toyota are basing this decision on performance that they should perhaps give him a little longer as he took a while at Renault to get things as he needed them; and after all the new Bridgestones are no real match for Michelin so far this year, all Bridgestone teams have struggled. However if it is the tyres that are causing the issue, there will be nobody better placed to forward the development of a fix than Vasselon.