So I tested a cloned a few versions and compared commits.
For me up to commit ab847968c66399f30328b2e9786248f32450d787 tool-bar worked.
Commit f6170fafcf59baba7083480cb6fb0638b388cd00 was suddenly when the tool-bar didn't even show up, but no errors.
And commit 551d2ce8cda320be0b881f164139bcdc97cbe9bd was when the error appeared.
TL;DR
Something broke and doesn't load right. If you want to get tool-bar working again then you could try to downgrade your version by downloading the build from an older version like v1.3.0 or the lastest working commit
I am too getting the same exact error, but I want to give a bit more information than the other issues.
Not 100% sure, but it looks like tool-bar can't generate the dist/iconsets.css file.
In the 551d2ce8cda320be0b881f164139bcdc97cbe9bd commit, if I revert the change done to the styles/tool-bar.less file, the error disappears, but the tool-bar doesn't show up.
So I tested a cloned a few versions and compared commits.
For me up to commit
ab847968c66399f30328b2e9786248f32450d787
tool-bar worked. Commitf6170fafcf59baba7083480cb6fb0638b388cd00
was suddenly when the tool-bar didn't even show up, but no errors. And commit551d2ce8cda320be0b881f164139bcdc97cbe9bd
was when the error appeared.TL;DR Something broke and doesn't load right. If you want to get tool-bar working again then you could try to downgrade your version by downloading the build from an older version like v1.3.0 or the lastest working commit