I'm running Jenkins v1.486 with envinject plugin version 1.72 being installed (but it's not configured/in use in the job where I get the error mentioned below). I noticed the following errors during job execution:

[EnvInject] - Loading node environment variables.
[EnvInject] - [ERROR] - SEVERE ERROR occurs: java.io.InvalidClassException: hudson.FilePath; local class incompatible: stream classdesc serialVersionUID = 1, local class serialVersionUID = -8164662025349363814
[...]
[EnvInject] - [ERROR] - SEVERE ERROR occurs: hudson.FilePath; local class incompatible: stream classdesc serialVersionUID = 1, local class serialVersionUID = -8164662025349363814

Once I disabled the envinject plugin the Jenkins job works fine again.
I guess it's an incompatibility between the plugin and the Jenkins version?
Let me know if you need any further information.