Ionic Serve on fresh ionic 4 project does not work - please help

Today i wanted to show a client some progress on a app i am writing.
I started -> ionic serve as usual but it stopped with this messag after a quick wait:

ng run app:serve --host= --port=8100
[ng] angular-cli[7128]: src\ Assertion `args[1]->IsString()’ failed.
[ng] 1: 00007FF676F821C5
[ng] 2: 00007FF676F5A056
[ng] 3: 00007FF676F5A10F
[ng] 4: 00007FF676F2E087
[ng] 5: 00007FF67738A37E
[ng] 6: 00007FF67738B5EC
[ng] 7: 00007FF67738A83D
[ng] 8: 00007FF67738A75B
[ng] 9: 000000EBF00D0361

[ERROR] ng has unexpectedly closed (exit code 134).

    The Ionic CLI will exit. Please check any output above for error

I started a fresh ionic 4 project to test if something was wrong with my project… same result.
I uninstalled and reinstalled ionic via npm. No change.
I reinstalled node.js -> no result.

Can anybody point me in the right direction please?

Short update. When i stard the CMD promot as administrator. Ionic server runs without any problems.
Still trying to find the solution. Anybody?