FSCM-TRM-TM: Creating positions for cross currency swaps

We are implementing SAP FSCM-TRM. When I try to create a cross currency swap (gsart= 62B; fhaart = 300) I get the error message:

TPM_TRL056: Currencies of flows and position CoCd:UK01 ValArea:001 ValCls:0003 Trans.:\INTERN\0063 are different.

I try to generate positions for each leg of the swap (in my case GBP and USD). I have configured update types DE1100+ and DE1100- for increase and reduction in nominal amount and I have assigned assigned position change categories: post (negative) purchase value, I have assigned a valuation procedure 7600 which is 1-step valuation procedure for foreign exchange. Do I have forgotten something?

Please let me know...