At the end of 2013, Esri moved ArcGIS 10.1 into 'Extended Support', which means that it will not be certified against new Operating Systems and environments.
As part of this transition, Esri have released a Quality Improvement Patch for ArcGIS 10.1 Service Pack 1 that aims to address performance and stability issues that have been encountered with this version of the software. A full list of the issues addressed in the patch can be viewed here.
The patch can be downloaded from the the following page at the Esri Patches and Service Packs website.
Esri UK recommends that any users of ArcGIS 10.1 Service Pack 1 apply this patch to take full advantage of the improvements that it brings to the software.