Can't open backoffice after installation into umbraco 7.12.4

[TwoMoreThings]

After installing UmbracoFlare via nuget I can't load the backoffice successfully.

I get 3 main errors, resulting in most of the backoffice being empty:

• /umbraco/backoffice/UmbracoApi/Section/GetSections returns a http error 417
• /umbraco/backoffice/UmbracoTrees/ApplicationTree/GetApplicationTrees?application=content&tree=&isDialog=false returns an exception, semmingly related to Umbraco.Core.Cache.HttpRuntimeCacheProvider.GetCacheItem(String cacheKey, Func1 getCacheItem, Nullable1 timeout, Boolean isSliding, CacheItemPriority priority, CacheItemRemovedCallback removedCallback, CacheDependency dependency)
• /umbraco/LegacyTreeJs?umb__rnd=fbd58e44ed201bfe971fd49c04fe05d5 results in access to path ..\config\trees.config' is denied

rolling back the changes in source control returns the back end to working, so I wouldn't expect this to be a folder/file permissions issue,

many thanks Tom