Scripts not loading on multisite installation

Hi,
I have a multisite installation with two sites. On the main site, all scripts (e.g. jquery.ui.tabs.min.js) are loading fine – but on the subdirectory site, they are NOT loaded. Do you have any idea, why this is not working?
I use WordPress v.3.7, Multilingual Press v.1.1.1 and jQuery UI Widgets v.0.31 (but it didn’t work with previous versions either).
Thanks!

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