Error 'Object reference not set to an instance of an object'

Question

I am trying to open a hydraulic model and I get the following message: Object reference not set to an instance of an object. I checked on the forum and I found that one of the solution would be to copy the .wtg and wtg.sqlite files on a separate folder. I tried even this method and still I have received the same error message. The version of HAMMER which I am using is V8i 08.11.06.58 64-bit.

Sushma Choure · Answer

Hello Sorinel, 
 Could you please inform the model you are trying to open is saved in which version of Hammer? 
 How to find the version a model was created in and last saved in 
 If the model is saved in higher than 08.11.06.58 version, then it cannot be opened directly but using other ways, please confirm. 
 Also try to compact database, File > Tools > Database utilities > Compact Database, or import database into a new model, File>Import>Hammer database, to see if that helps. 
 If required please upload model files for our testing. 
 Sharing model files.

Sushma Choure · Answer

Hello Sorinel, 
 The model you are trying to open is saved in higher version 10.02.00.43, so it cannot be opened directly in the lower version that you have 08.11.06.58. 
 What you could do it upgrade to 10.02.00.43 version or to the latest version. Latest version can be downloaded using version below. After upgrading to 10.02.00.43 or latest version you can open that model directly. 
 Downloading OpenFlows | Hydraulics and Hydrology Software 
 
 However you appear to have Non-SELECT contract, so upgrade will not be possible unless you upgrade to SELECT. 
 In that case you may ask your client to export the model from 10.02.00.43 version into EPANET format or shapefile formats, then you can import that EPANET file in lower version of Hammer 08.11.06.58. 
 This is explained in detail in below wiki, please go through it. 
 Model backward / forward compatibility