Can't launch without a power plant ???????

[Dragonmaster]

I have very strange troubles. If i want-launch to space from a POB, it always says: Your Ship must have a mounted power plant to launch. I have no idea what this means. At first i thought i need a other engine. But it don't works and this is very strange because i have exactly the same ship on this Base with exactly the same equipment on it. And on the second ship everything is working fine.
Can anyone tell me please what it means: You can't launch without a mounted power plant?

Thanks in advance

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