CSV Import IssueUtils.createIssue(...) throws exception

Using the import_csv.jsp throws the following:
javax.servlet.ServletException: One of the fields (projectId, issuetype, summary) is not present or of the wrong type

I read the other issues "CVS Import broken", which helped me to get a bit ahead. Still this is blocking any progress moving to JIRA.

The Map passed contains (type information in [Brackets]):
assignee=reck [String]
reporter=reck [String]
projectId=10000 [Long]
issueType=1 [String]
summary=BSIfcAdapter shall use OT-BS for nameserver resolving [String]
description=OTBS.1 [String]
priority=4 [String]

I tried using a String for projectId and Long for issueType, with no success. Therefore the Exception is misleading.

Catching the exception in the JSP and printing it there I get:
at com.atlassian.jira.issue.IssueUtils.createIssue(IssueUtils.java:94)
at com.atlassian.jira.issue.IssueUtils.createIssue(IssueUtils.java:80)
at org.apache.jsp.import_csv_jsp._jspService(import_csv_jsp.java:239)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:137)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:204)
...

Please help me out with knowledge of what the source code expects.

THX,
Christoph