Trying to save an xslt file on a shared hosting, receiving this error:

System.Security.SecurityException: Request for the permission of type 
'System.Security.Permissions.EnvironmentPermission, mscorlib, 
Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' 
failed.

umbraco.presentation.webservices.codeEditorSave.SaveXslt(String 
fileName, String oldName, String fileContents, Boolean ignoreDebugging)

The action that failed was:
Demand
The type of the first permission that failed was:
System.Security.Permissions.EnvironmentPermission
The Zone of the assembly that failed was:
MyComputer

I've replaced the Lucene assembly (http://umbraco.codeplex.com/workitem/28080) but still receiving this error. Application is running in medium trust perfectly, except parsing xslt files, file is saved correctly.

Umbraco v 4.5.1 + MySql