Charles certificate install problem

Hi,

I am trying to install Charles certificate in Nvidia Shield but I am receiving this error:

06-13 10:30:42.015 701-3612/? I/ActivityManager: START u0 {act=android.intent.action.VIEW dat=file:///storage/emulated/0/Download/charles-proxy-ssl-proxying-certificate.pem typ=application/x-pem-file flg=0x10000000 cmp=com.android.certinstaller/.CertInstallerMain} from uid 2000 on display 0

06-13 10:30:42.081 17232-17232/? E/CertInstaller: Failed to read certificate: java.io.FileNotFoundException: /storage/emulated/0/Download/charles-proxy-ssl-proxying-certificate.pem (Permission denied)

Do you know if there is a way to install a certificate?

Thanks in advance!
JC

Giving more info, I am also receiving this error when I try to install the certificate from a browser:

06-13 11:00:50.563 23683-23683/? E/ActivityThread: Activity com.android.certinstaller.CertInstaller has leaked ServiceConnection com.nvidia.NvAccSt.NvAccStCapture$NvAccStClient$1@89a5a03 that was originally bound here
android.app.ServiceConnectionLeaked: Activity com.android.certinstaller.CertInstaller has leaked ServiceConnection com.nvidia.NvAccSt.NvAccStCapture$NvAccStClient$1@89a5a03 that was originally bound here
at android.app.LoadedApk$ServiceDispatcher.(LoadedApk.java:1336)
at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:1231)
at android.app.ContextImpl.bindServiceCommon(ContextImpl.java:1529)
at android.app.ContextImpl.bindServiceAsUser(ContextImpl.java:1509)
at android.content.ContextWrapper.bindServiceAsUser(ContextWrapper.java:643)
at com.nvidia.NvAccSt.NvAccStCapture$NvAccStClient.connect(NvAccStCapture.java:273)
at com.nvidia.NvAccSt.NvAccStCapture.(NvAccStCapture.java:66)
at android.view.ViewRootImpl.(ViewRootImpl.java:481)
at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:331)
at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:93)
at android.widget.Toast$TN.handleShow(Toast.java:442)
at android.widget.Toast$TN$1.run(Toast.java:342)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6120)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

Thanks!