Error creating resource via the api

I try to create a resource via the api with the following code:

aResource = aCollection.createResource(fileName, propMap, aContent)

The objects aCollection, fileName, propMap and aContent are all filled and valid.

As a result i always run in the following ResourceException

com.sapportals.wcm.repository.ResourceException: Cannot assign an empty string to host variable 6.

Let this message rings a bell by somebody??

We are on NW04 SPS17.

Regards,

Thomas