FTW Controller described a probable loss of separation event when confusion regarding an IFR release prompted a clearance to remain in the traffic pattern and the weather changed from VFR to IFR.

Narrative

After receiving a release on a BE40 via the rundown list; I cleared the BE40 for takeoff from Runway 16. As he departed; his call sign began to flash indicating he was not released. I then had him squawk 1200 and enter left traffic to confirm release. The previous METAR showed the field VFR. I had not been informed by Flight Data that a special had been put on and the field was now IFR with a ceiling of 800FT overcast. I asked the pilot if he had the field in sight and he told me he did. After confirming with D10 that he was released; the pilot told me he lost the airport and was receiving an RA. I called D10 back and was told to turn him south. I then issued a left turn of 160. D10 called back and told me to expedite his turn; in which I did. I then gave the pilot an altitude of 3;000 FT as instructed and switched him to Departure. The pilot later called me back on frequency to see what the problem was and I informed him there had been some confusion on his release status and told him I was sorry about the confusion. It was my belief at the time is that it would be safer to put him on the downwind and keep him close because I felt his release had been canceled suddenly and did not know if it was for an imminent situation. We as a team in the Tower need to make sure everyone knows if there is a weather change. Coordination between controllers needed to be better in this situation as well as awareness on all positions. From the technical side; we need to look at why; after the aircraft was released; it began to flash again indicating he was not released.