Workflow runs as system administrator, but no longer with the security role

Hello,

My workflow, developed in CRM2011 - Online, gives no error when run as systemadministrator but gives following error ErrorCode>-2147220970</ErrorCode> when run under the other defined roles.

Upon creation last year the workflow worked fine but after some updates from Microsoft, I suppose, we get this message.

Has anyone an idea how to takle this problem ?

Thx