Which version of DNN are you using?
If it is 4.4.1 some dll files were missing from the install version which maybe causing this error.
the same problem occurred here:
How to fix the [DROPDOWNACTIONS] token bug in DotNetNuke 4.4.1If you download version 4.5.1 go to the bin folder and copy this dll file into the bin folder of your 4.4.1 installation it should solve your problem:
DotNetNuke.DNNTreeNavigationProvider.dll